题目内容：

根据汉语提示完成句子，每空一词。

1.I think everything will ________ ________ (免费的)．

2.In the future, people will ________ ________ ________ (活到) 200 years old.

3.There will be fewer trees and the environment will be ________ ________ ________ (处于极大的危险之中

4.Everyone should ________ ________ ________ (参与) in saving the earth.

5.如果建筑物倒塌，里面又有人，他们会很快赶过来。

If buildings ________________ with people ________，they will come soon.