根据句意及所给中文提示或英文解释，写出句中所缺单词

1. Our earth is getting more and more ________(拥挤) because of the increase of people.

2. Sandy was late for school this morning because her bicycle went ________(毛病).

3. Jumping on Mars will be ________(危险) because we easily jump too high and flew away.

4. I think an air tank is the most important thing for an ________(宇航员).

5. We wear ________(特殊的) costumes with masks.

6. Simon wants to c________(to become different) his diet because he wants to healthier.

7. They have made a plan to clean up the p________ rivers.