1) ______________________________

To remove dirt or stains from something.

2) ______________________________

This type of precipitation is caused by pollution and is harmful to plants, animals, bodies of water, and buildings.

3) ______________________________

This is another term for global warming.

4) ______________________________

A person who helps or offers to do something without getting paid.

5) ______________________________

The protection and more efficient use of natural resources.

6) ______________________________

This occurs when running water, sea waves, wind, or glaciers pick up and carry away materials from the earth's surface.

7) ______________________________

Harmful substances that are released and make our planet dirty, noisy, or unhealthy.

8) ______________________________

The constant recycling and movement of water on Earth. Energy from the sun, plants, or animals causes water to evaporate. The water vapor rises in the atmosphere to form clouds. Rain returns the water from clouds back to the earth's surface.

9) ______________________________

A unit of electric power, equal to one joule of work per second.

10) ______________________________

Thermal energy that travels in waves and can pass through empty space as well as some objects.

11) ______________________________

A solid, hard black mineral that burns and gives off heat.

12) ______________________________

A plant with leaves, roots, and a single, woody trunk.

13) ______________________________

A metal container.

14) ______________________________

The place or type of environment where an animal or plant naturally lives or grows.

15) ______________________________

The invisible mixture of gases we breathe.

16) ______________________________

We must breathe this gas in the air to survive.

17) ______________________________

This covers most of the earth's land, and is made up mostly of disintegrated rocks.

18) ______________________________

A type of potential energy that can be burned to supply heat, such as wood.

19) ______________________________

A type of fuel used in cars with internal-combustion engines. This is made from petroleum.

20) ______________________________

Manufacturing companies and other businesses.