1. The volunteers collected 20 bags of garbage along 100 yards of the lake’s .

2. Cities issue health alerts when the amount of in the air can cause problems for people with breathing difficulties.

3. The school buses took routes to avoid the road reconstruction on the city’s main street.

4. The provides population information, such as where people live, how many people they live with, and what they do for a living.

5. The roots of trees and grasses help hold soil in place and prevent caused by wind and water.

6. During a , crops may die because they do not get the water they need to grow.

7. The citizens listened to the debate identifying the pros and cons of the plan to build a new shopping center.

8. One way to or avoid wasting energy is to turn off lights when you leave a room.

9. A car’s engine the chemical energy of fuel into the mechanical energy needed to run the car.

10. Like coal and oil, natural gas is a source of energy that cannot be replaced.

11. Our use of resources such as trees is if we do not use the resources faster than they can be replaced.

12. Coal, trees, water, and metals such as iron are examples of natural that people use to meet their needs.

13. The desert is the natural of cactuses that can live in very dry places.

14. The of polar bears may worsen if ice floes in the Arctic melt.

15. The populations of alligators after laws were passed to protect these animals.