1. Crop .......... is when small, low-flying planes release chemical pesticides onto large crops like grain fields. These planes are able to evenly release a lot of pesticides at one time but the job is dangerous because the pilots have to fly so close to the ground.

2. An oil .......... is when a large amount of oil is accidentally released into a natural environment. They are very dangerous because the oil contaminates the area, such as an ocean habitat, and living things are directly and indirectly affected for years to come. These accidents are so harmful because it's very difficult to uncontaminate the area.

3. The .......... forests of the world are hot and humid most of the time and are usually found in tropical countries. These areas are large, have a lot of diverse plant and animal life and produce a lot of oxygen. These are invaluable areas that we must strive to protect.

4. .......... energy is a type of energy source that humans can harness and use on a continuous and indefinite basis. Energy sources such as solar and wind power are examples of this.

5. .......... water comes out of faucets in homes and businesses. This water source is cleaned, filtered and monitored by municipal water stations before it is released into homes.

6. When factories and power plants burn fossil fuels like coal and gas, a dark, sticky, powder-like substance is released into the environment. It's mostly made up of carbon elements and is called .......... . People first began to notice this during the Industrial Revolution that took place in Europe.

7. .......... is a petroleum-based energy source that is mainly used to power combustion engines like those found in cars and trucks.

8. Scientists study and monitor geo.......... areas because a lot of heat is produced in these zones. This refers to the extreme heat sources found under the earth's crust.

9. In recent years, ..........-fishing has become a real problem. This refers to fishing practices that deplete natural seafood sources so fast that the natural environment doesn't have enough time to re-populate the area on its own.

10. Many companies and scientists are trying to develop better ways of using existing energy sources. For example, they want to develop new machines that can do twice the work using only half of the energy amount that was once used. This is called improving energy .......... .