Welcome to the Member Resources page.  All the resources on this page are available to Members of the site.    Everyone can view the list and range of resources, but unless you are a member you will be unable to access them.

Why become a member?

  • Get access to a range of tested Earth science classroom activities and teacher guides,
  • Get access to posters, rock charts, and more,
  • Get access to video clips and full classroom video-based modules,
  • Get discounts on all our educator Field Adventures (does not include Geocaching trips)
  • Get discounts on other GEOetc services.

Who can become a member?

  • Teachers, educators, college students, homeschoolers, retirees…anyone who has a passion for Earth science!

To become a member, you can click on any of the resources below and follow the ‘Register’ links or join up here.

So many resources...scroll down or click on a button to jump to a section.

GEO Quiz World

Have your students take a quick 10-question multiple choice quiz on a range of Earth science topics.  Be sent an email of how they did in the quiz.  Take the quiz yourself to test your own knowledge.

Activities and Resources

You can narrow down your search by selecting the Topic and/or Type of resource.

To return to the full listing, just unselect the boxes.

Magma Paperclips

Magma Paperclips

Have your students model the eruption changes due to the different chemistry of magma.  Using paperclips and a plastic contain, students time how long it takes for paperships to move …
Eruption Styles

Eruption Styles

Work out the eruption style of two volcanoes using eye witness accounts and reading the data from a diagram.  Additional internet research may be required. An extension activity is included …
Writing Prompts

Writing Prompts

Here are some writing prompts/essay questions that you can use with senior students or as research project for younger grades.  The length of the responses is up to you – …
Granite Mineral Search

Granite Mineral Search

This is an introductory activity on minerals. It aims to show students that rocks are made of different minerals, which have properties that can be used to distinguish them. Have …
Earth's Rock Cycle Poster (Free)

Earth’s Rock Cycle Poster (Free)

Print your own Geoscience – downloadable PDF file.”Earth’s Rock Cycle”It is US Letter in size – but can be scaled on your printer to any size you like.Download PosterLooking for …
Earth's Rock Cycle Poster

Earth’s Rock Cycle Poster

Print your own Geoscience – downloadable PDF file. “Earth’s Rock Cycle” It is US Letter in size – but can be scaled on your printer to any size you like …
Rock Cycle Proceses (Complex)

Rock Cycle Proceses (Complex)

Have your students complete a complex rock cycle diagram by identifying the major processes. This activity uses a complex diagram that separates extrusive and intrusive rocks and foliated and non-foliated …
Rock Cycle Rock Types (Complex)

Rock Cycle Rock Types (Complex)

Have your students complete a complex rock cycle diagram by adding the major rock types. This activity uses a complex diagram that separates extrusive and intrusive rocks and foliated and …
Rock Cycle Rock Types

Rock Cycle Rock Types

Have your students complete a simple rock cycle diagram by adding the major rock types. This straightforward activity could be used as an introduction to the Rock Cycle.  It could …
Rock Cycle Processes

Rock Cycle Processes

Have your students complete a simple rock cycle diagram by adding the processes that form the three major rock types – melting, weathering/erosion/deposition, or heat and/or pressure. This straightforward activity …
Mineral Charts

Mineral Charts

Have your students research the mineral properties of hardness, luster, cleavage/fracture etc. Then use a table of 12 common minerals and some descriptions to identify three unknown minerals. The object …
Mineral Color

Mineral Color

Have your students work out how many minerals they can see in an image. They may be surprised at the answer! The object of the activity is to show how …
Gold Streak

Gold Streak

Students do some online research to discover the color of the streak of minerals commonly mistaken for gold. They then use their new knowledge to identify a sample showing a …
How hard is it?

How hard is it?

Have students work out the relative hardness of common items found in your classroom (you can select five items such as pencil lead, chalk, copper coin, knife, wood etc). Then …
Sedimentary Shuffle

Sedimentary Shuffle

Have students classify sedimentary rocks into clastic, chemical, or organic based on their mode of formation. Have them discuss in a group why each one needs to go into the …
Seismic Shadow

Seismic Shadow

Have students listen to this podcast on how seismic waves are used to discover the structure of the Earth as a way to introduce this topic. Then use this simple …
Earthquake - Data

Earthquake – Data

Have your students examine data about earthquakes that have taken place between 1900 and 2023.   The data contains only earthquakes of magnitude 5 and greater.    The data is below …
Tsunami - Data

Tsunami – Data

Have your students examine data about tsunamis that have taken place between 1900 and 2023.   The data is below in three formats so you can have students load into a …
Volcanic Eruptions - Data

Volcanic Eruptions – Data

Have your students examine data about volcanic eruptions that have taken place between 1900 and August 2024.   The data is below in three formats so you can have students load …
Sock Faults

Sock Faults

Let’s use socks with patterns to model fault types and calculate displacement.   Here are two images of different types of faults (normal and reverse/thrust) faults being modeled using the patterns …
What soil type?

What soil type?

A simple classification of soil is based on the type of rock materials they contain – from very sand-rich soil through to very clay-rich soil.  This is a simple activity …
Plate Tectonics Battleships

Plate Tectonics Battleships

Have your students play the classic ‘battleship’ game , but using earthquake and volcano locations on Earth.  At the end of the game, can they see patterns?   Do the patterns …
What is doing it - Physical Weathering

What is doing it – Physical Weathering

Can your students work out what the major physical weathering force is acting in a series of photos?  What evidence can they cite for their conclusions? Downloadable activity (Download) Suggested …
Freeze and thaw - physical weathering demo

Freeze and thaw – physical weathering demo

This is a demonstration (or group activity) to show students how repeated freeze and thaw of a rock sample can start to break it down.  This is an example of …
Soil in a jar

Soil in a jar

Have your students collect and examine the components of soil in a jar.  Students will need to have a jar for each sample, and can use this to see the …
How old was the tree?

How old was the tree?

Have your students use a real image of a tree to work out its age by counting tree rings. This can be a simple activity for them to do alone, …
Flow vs Sill

Flow vs Sill

Have your students look for evidence of an outcrop of basalt in a cliff to determine if it is a flow or a sill.  They also ponder what other evidence …
Iceland - damage in Grindavik photos

Iceland – damage in Grindavik photos

Grindavík is a fishing town on the Southern Peninsula of Iceland. It is one of the few towns with a harbor on this coast and is an important fishing port …
Hekla History

Hekla History

Have your students examine the dates for the past eruptions of the volcano Hekla in Iceland.  Using the data they can work out the time between those historic eruptions, and …
What's happening on Sebago Beach?

What’s happening on Sebago Beach?

Have your students watch a 20-second video (let them watch it as many times as they like), then describe what they see happening to the sediments (sand and gravel) on …
Count the columns

Count the columns

Have your students work out the average number of sides on basalt columns.  This is an “Earth science meets math” activity. Students have to determine how many sides there are …
Graptolite Games

Graptolite Games

Have your students read a time/species distribution table to work on the age ranges of some of the extinct fossils known as graptolites.  They then use this skill to work …
Toilet Paper Timelines

Toilet Paper Timelines

Have your students work to build timelines using toilet paper to represent recent events.  They then can calculate how many rolls of toilet paper they will need to represent some …
Time Speedometer

Time Speedometer

Have your students work complete a simple table of Earth processes (events) from very fast (seconds to minutes) to very slow (millions to billions of years).  A list of 15 …
Divergent Dilemma

Divergent Dilemma

Have your students work on the relative movement of four tectonic plates at an offset spreading ridge (divergent plate boundary).  They complete a simple table and then draw conclusions about …
Metamorphic Thermometer

Metamorphic Thermometer

Print your own Metamorphic Thermometer Poster – downloadable PDF file. Download Poster …
What Schist?

What Schist?

Have your students identify the metamorphic index minerals in three schist samples.  Then, using the Metamorphic Thermometer chart, work out the lowest temperature that rock was placed under during metamorphism …
iPhone Index Fossils

iPhone Index Fossils

Have your students examine how changes in iPhone design over time may lead an iPhone to become an index fossil in the future. iPhones have changed in size, shape, type …
Tectonicland

Tectonicland

Students have to read radioactive decay curve graphs to find the ages of samples of rocks collected from the planet Tectonicland.  They then use that data to see if two …
Ocean Floor Ages

Ocean Floor Ages

Have your students find themselves on a map that shows ocean floor ages and then read the age of the ocean floor nearest to them.   Then they can search for …
Name the Plates

Name the Plates

Have your students correctly label the major tectonic plates and some of the minor plates on a simple world map.  They may need a labeled world map to know the …
Varves

Varves

Have your students examine a section of varves (in an actual varved shale from Antarctica) and identify the summer and winter layers.  They can work out the average thickness of …
Zircon Dating

Zircon Dating

Have your students work out the ages of zones in a zircon mineral by reading a radioactive decay curve.  They then need to calculate the average age of the crystal …
Earth's Interior Layers

Earth’s Interior Layers

Have your students label a diagram of the Earth’s interior layers – on one side are the chemical layers (Crust, Mantle, Core), and on the other side the mechanical layers …
Cruise of the RV Oakley

Cruise of the RV Oakley

Have your students plot water depth data from a ship’s survey as it passes over plate tectonics features such as a continental shelf, deep ocean trench, guyot, and mid-ocean ridge.  …
Earth science is HOT Poster

Earth science is HOT Poster

Print your own Geoscience – downloadable PDF file. “Earth science is better than COOL.  Earth science is HOT” The image is of the 2022 summit eruption of Kilauea, Hawaii. It …
Present is key to past Poster

Present is key to past Poster

Print your own Geoscience – downloadable PDF file. “The present is the key to the past.” is a quote by Charles Lyell which he published in his thought-changing “Principles of …
Stromatolite Poster

Stromatolite Poster

Print your own Geoscience – downloadable PDF file. “For the first half of geological time our ancestors were bacteria.” is a quote by Richard Dawkins alluding to how long the …
Geologic Time Poster

Geologic Time Poster

Print your own Geologic Time poster – downloadable PDF file. It is 18 inches X 24 inches – but can be scaled on your printer to any size you like …
Compass Reading

Compass Reading

Have your students practice reading directions from a compass – cardinal points as well as bearings.  This is an important skill for any students wanting to do a field-based science …
Earth's Plate Tectonic Features

Earth’s Plate Tectonic Features

Have your students use this Google Map that shows different features on Earth that are related to Plate Tectonics – mid-ocean ridges, deep trenches, and volcanoes related to subduction.  The …
World Earthquakes by Depth

World Earthquakes by Depth

Have your students use this Google Map of a month of the globe’s Earthquake data to see how earthquakes are distributed by depth.  This is a great way to show …
Gravestone Project - teachers guide

Gravestone Project – teachers guide

TEACHERS GUIDE This is a guide to help you guide students through visiting and collecting gravestone data. Background Your local graveyard or cemetery is a wonderful place to collect data …
Lava Risk - interpreting a lava risk map

Lava Risk – interpreting a lava risk map

Have your students read data from a USGS lava risk map and interpret the most dangerous locations and where they would want to locate. This activity would take students 15-20 …
Thunder Island - volcanic eruption simulation

Thunder Island – volcanic eruption simulation

An in-class simulation where students play the role of scientists providing information about the possible eruption of volcanoes on an island. You split your glass into these groups: Deformation team …
World River Quest

World River Quest

This activity has your students visiting five rivers around the world using Google Maps or Google Earth.  They can zoom in and out on the river and record their observations …
Banded Iron Formation Chemistry

Banded Iron Formation Chemistry

Banded Iron Formations (BIFs) make up 60% of the Earth’s iron ore deposits.  They are ancient sedimentary rocks that are made up of fine layers (millimeters to centimeters thick), with …
Crystal Chemical Zones

Crystal Chemical Zones

As a crystal grows in molten rock, the chemistry of the crystal changes as the molten material becomes depleted of elements (ie. elements are removed from the melt into the …
Reading Ternary Diagrams

Reading Ternary Diagrams

A ternary diagram is a great way to display data that has three variables.  This activity gives students experience reading and adding data to a ternary diagram. I use this …
Chemical Weathering of Feldspar

Chemical Weathering of Feldspar

Feldspar, one of the major rock-forming mineral families, breaks down chemically to form clay when it is exposed at the surface to the elements. In this activity, students are trying …
Crustal Elements

Crustal Elements

The Earthy’s crust is made up of an array of the known elements – but your students may be surprised at which of the elements make up the bulk. This …
Earthquakes - Find Detritus

Earthquakes – Find Detritus

One of the most important concepts when teaching students about measuring earthquakes is to have them understand that we can calculate the distance from a point that an earthquake took …
Trilobite ID

Trilobite ID

Have your students describe a fossil trilobite using a sketch, count trilobites in a sample and even draw a trilobite from a description. While this is fossil-based, this is an …
Structure of Earth

Structure of Earth

Have your students summarize the basic structure of the Earth – crust, mantle, outer core, and inner core – on this blackline master.  There is room for them to add …
Climeworld Eruption

Climeworld Eruption

Have your students map the spread of volcanic products from eruptions on the planet Climeworld.  They will plot on a map a spread of the plumes and see how volcanoes …
Occupation Ages

Occupation Ages

Have your students use carbon 14 data and a radioactive decay curve graph to work out the differences between occupation ages of an Aboriginal tribe on islands in northern Australia …
Terrace Temperatures

Terrace Temperatures

Have your students use foram (fossil) data to work out the changes in sea level in a bay as shown in terraces.  This activity has them using map data, graph …
Tree ring climates

Tree ring climates

Have your students use tree ring data to examine climate change.  The activity has students see the variation in data between two trees located in different sites in a valley …
Iceman - ice core forensics

Iceman – ice core forensics

Have your students use ice core data to work out the age of a skeleton found in the ice and describe the climate record shown in the ice core. This …
Plate Tectonic 3D Models

Plate Tectonic 3D Models

Have your students construct 3D cut-out interactive paper models of : Sea Floor Spreading Subduction Zone The package also includes two tennis-ball globes (supply your own tennis ball) – one …
Earthquakes - reading time & distance (P&S) graph

Earthquakes – reading time & distance (P&S) graph

Can you read an earthquake time-distance graph Have your students read a simple time-distance graph that shows the relationship between the arrival times of P and S earthquake waves and …
Where to build the Hospital - Lava risk

Where to build the Hospital – Lava risk

Where to build the hospital – Lava Risk Mapping Have your students take on the role of a volcano risk scientist and interpret a map and table to provide a …
Thunder Island - a volcanic eruption simulation

Thunder Island – a volcanic eruption simulation

Thunder Island – a simulation using data. Have your students work in teams to analyze data and provide advice about the possible eruption of volcanoes.  This is a lively, exciting …
Earthquake Magnitude

Earthquake Magnitude

Earthquakes are an amazing phenomenon on our planet.  They are caused by the build-up of energy in moving slabs of rock which finally break to release the energy.  The breaking, …
Subduction Worksheet

Subduction Worksheet

Plate Tectonics – Subduction Zone worksheet Have your students research and then label the features of a Subduction Zone using this easy to use worksheet.  Major features are included – …
Crust Types Worksheet

Crust Types Worksheet

Plate Tectonics – Types of crust worksheet Understanding the differences between the two types of crust on Earth is fundamental to understanding Plate Tectonics.   This activity sheet allows students to …
Glacial striations (DEMO)

Glacial striations (DEMO)

Description : This demonstration shows how glacial grooves and striations are made by the passing of glacial ice over the underlying bedrock.  Students can see the striations made in real …
Icebergs and sea level rise (DEMO)

Icebergs and sea level rise (DEMO)

Description : A demonstration that shows the relationship between sea ice melting and sea level change.  Students are asked to predict if a melting iceberg will make sea level rise, …
Using Gravestones

Using Gravestones

Graveyards and cemeteries are wonderful places for students to learn about geoscience, mathematics, history, language and so much more.  As a way to integrate all these topics into one field …
Lava in Lihue - Role play activity

Lava in Lihue – Role play activity

Description : A classroom role-play activity where students play the role of various town people when their town is being threatened by an active lava flow.  This activity allows students …
Cross Section Activities

Cross Section Activities

Here are a series of cross section activities that you can use with your students. Each activity has a color version, a black & white version, and a suggested solution.  …

Discussion Starters

Short videos that can help you start discussions with your students.

What are these washed up rocks? (Pumice)

What are these washed up rocks? (Pumice)

These rocks are found in the high tide zone of beaches on the coast of Australia.  They are very light in color and weight. How do you think they formed? …
What is making the rocks look like this? (Weathering)

What is making the rocks look like this? (Weathering)

Sandstone layers on the coast are weathering to form this strange pattern of holes. What do you think is happening to cause this type of weathering? What evidence would you …
What is cutting through those rocks? (Igneous intrusion)

What is cutting through those rocks? (Igneous intrusion)

Layers of almost horizontal sedimentary layers of sandstone are cut by a vertical structure.  What could that be? What evidence can you see to back up your thoughts? What evidence …
How did that rock get here? (Tsunami)

How did that rock get here? (Tsunami)

Sitting somewhat alone on a rock platform well away from any cliffs is this huge block of rock – the size of a small car! How could it have been …

Posters

 

Rock Posters

Print your own rock posters – downloadable PDF file.  4 full-color pages.  These are 2 pages wide (17 inches/43 cm) and 2 pages high (22.7 inches/58 cm).

Sedimentary

Metamorphic

Igneous

Rock Cards

This is a new and growing resource for your teaching.  Each rock card provides you with images of the outcrop, an interactive hand specimen (you can zoom in and rotate), and a hand lens view.

Rock card: Gneiss - Gilead, NH, USA

Rock card: Gneiss – Gilead, NH, USA

Where is this from? This gneiss is from Gilead, New Hampshire, USA What is it? The gneiss is part of …
Rock card: Pegmatite vein - Windham, ME

Rock card: Pegmatite vein – Windham, ME

Where is this from? This pegmatite vein is part a granite body in North Windham, Maine, USA.  (N 70.4491, W …
Rock card: Basalt dike - Windham, ME

Rock card: Basalt dike – Windham, ME

Where is this from? This dike is intruded into a granite body in North Windham, Maine, USA.  (N 43.8393  W …
Rock card: Granite - Windham, ME

Rock card: Granite – Windham, ME

Where is this from? This granite outcrop is in North Windham, Maine, USA.  (N 70.4491, W 43.8393) What is it? …
Rock card: Basalt - Hawaiian lava flow

Rock card: Basalt – Hawaiian lava flow

Where is this from? In 2018, Kilauea volcano on the Big Island of Hawaii erupted on its lower east rift …

 

The Earth Science Teacher

The Earth Science Teacher was the member journal of GEOetc.   It was published a few times a year and contained background information, teaching resources, links to member resources, and more.

It was discontinued in 2024.

TESTeacher 4.4 - Sedimentary Rocks

TESTeacher 4.4 – Sedimentary Rocks

In this Edition In this issue, we look at sedimentary rocks and how they are classified into clastic, chemical and …
TESTeacher 4.3 - Erosion

TESTeacher 4.3 – Erosion

In this Edition In this issue, we look at Erosion including that caused by gravity, water, wind and ice. Download …
TESTeacher 4.2 - Chemical Weathering

TESTeacher 4.2 – Chemical Weathering

In this Edition In this issue, we look at Chemical Weathering including hydration, hydrolysis etc Download this issue …
TESTeacher 4.1 - Physical Weathering

TESTeacher 4.1 – Physical Weathering

In this Edition In this issue, we look at Physical Weathering – water, wind, ice, salt, plants etc. Download this …
TESTeacher 3.4 - Igneous Intrusions

TESTeacher 3.4 – Igneous Intrusions

In this Edition In this issue, we look at Igneous Intrusions, how magma forms etc. Download this issue …
TESTeacher 3.3 - Rock Relationships

TESTeacher 3.3 – Rock Relationships

In this Edition In this issue, we look at Rock Relationships – and provide links to cross-section activities. Download this …
TESTeacher 3.2 -  EarthCaching

TESTeacher 3.2 – EarthCaching

In this Edition In this issue, we look at EarthCaching and provide links to download the full Educators Guide to …
TESTeacher 3.1 -  Metamorphic Rocks

TESTeacher 3.1 – Metamorphic Rocks

In this Edition In this issue, we examine metamorphic rocks – minerals, pressure, metamorphic grade, and more. There are links …
TESTeacher 2.4 -  Glaciers

TESTeacher 2.4 – Glaciers

In this Edition In this issue, we discuss the processes of the formation of glaciers and then examine the evidence …
TESTeacher 2.3 -  Iceland volcanoes

TESTeacher 2.3 – Iceland volcanoes

In this Edition In this issue, we discuss the processes (divergent plate boundaries and a hot spot) and how they …
TESTeacher 2.2 -  Divergent Plate Boundaries

TESTeacher 2.2 – Divergent Plate Boundaries

In this Edition In this issue, we divergent plate boundaries – mid ocean ridges, Iceland, East African Rift Zone. There …
TESTeacher 2.1 Fossils

TESTeacher 2.1 Fossils

In this Edition In this issue, we examine fossils – how they form, types of preservation and how they are …
TESTeacher 1.4 Deep Time

TESTeacher 1.4 Deep Time

In this Edition In this issue, we examine the concept of deep time and how to introduce it to your …
TESTeacher 1.3 Mineral Identification

TESTeacher 1.3 Mineral Identification

In this Edition What are the physical properties you can use in your classroom to identify minerals?   Learn about the …
TESTeacher 1.2 Volcanoes

TESTeacher 1.2 Volcanoes

In this Edition Volcanoes – and an approach to teaching them in your classroom from magma chemistry to eruption style …
TESTeacher 1.1 Earthquakes

TESTeacher 1.1 Earthquakes

In this Edition Earthquakes and how to teach them in your classroom Member Speaks – Kate Lefever tells how she …

Videos

Mathematics on an Active Volcano

Mathematics on an Active Volcano

Want to make your teaching and learning of mathematics more exciting? What could be better than learning about the use …
Engineering on an Active Volcano

Engineering on an Active Volcano

Want to make your teaching and learning of engineering exciting? What could be better than learning about the use of …
Technology on an Active Volcano

Technology on an Active Volcano

Want to make your teaching and learning of technology exciting? What could be better than learning about the use of …
Science on an Active Volcano

Science on an Active Volcano

Want to make your Science teaching and learning exciting? What could be better than learning about the science of an …

Watcha Thinkin

Watcha Thinkin is a way to start discussions in your classroom about an Earth Science topic (aligned to the NGSS Storyline process).

Watcha Thinkin - Volcanoes

Watcha Thinkin – Volcanoes

Watcha Thinkin is a way to start discussions in your classroom about an Earth Science topic (aligned to the NGSS Storyline process).   This Watcha Thinkin is for Volcanoes. Suggested flow Watch video with the prompt ‘What do you notice?’ Students …

Writing Prompts

My story - Outrun the lava

My story – Outrun the lava

Teacher Notes In 1974 lava from the Mauna Ulu eruption on the volcano Kilauea in Hawaii, USA cut a road …
My story - Lava tube

My story – Lava tube

Teacher Notes Nāhuku (once called Thurston Lava Tube) was formed in an eruption 500 years ago on the volcano called …
My story - Coconut Sprout

My story – Coconut Sprout

Teacher Notes Someone planted this coconut in a newly formed black sand beach that formed when lava poured into the …
My story - Volcanic crater

My story – Volcanic crater

Teacher Notes This is Kerid crater – a volcano explosive crater that formed in Iceland around 6,500 years ago.  It …
My story - Horses to the falls

My story – Horses to the falls

Skogafoss is one of the most famous waterfalls in Iceland.   It is fed by a melting icecap (glacier) a few …
My story - Falling column

My story – Falling column

Teachers Notes Two hopeful geologists act like they are holding up a basaltic column on the south coast of Iceland.  …
My story - Boy strikes it rich

My story – Boy strikes it rich

Teachers Notes While collecting minerals on Mount Apatite in Minot, Maine , USA, Oliver found what he thought was an …
My story - In the vent

My story – In the vent

Teachers Notes These students are sitting in the 1969 eruptive vent of Kilauea volcano on the Big Island of Hawaii, …
My story - Devils Coach House

My story – Devils Coach House

Teachers Notes This is the Devils Coach House – a very large limestone cave at Jenolan, New South Wales, Australia.  …
My story - Diamond Beach

My story – Diamond Beach

Teachers Notes This is a photo taken on Diamond Beach in Iceland.   A nearby glacier is calving off icebergs into …

Earth & Beyond

We are building a full curriculum – and will release new lessons here.

Exploring Earth's Layers: Core, Mantle, and Crust

Exploring Earth’s Layers: Core, Mantle, and Crust

A lesson plan and resources to introduce your students to the internal layers of the Earth.   Students will understand the Earth’s composition and its division into layers: crust, mantle, outer core, and inner core. Students will be able to define …

GEOetc on TickTok

If you are looking for some Earth Science on TikTok – then check out the videos i record while traveling around the planet.     You will find the latest on the TikTok app.  Just search for @GEOetc