题目内容：

根据括号内的汉语提示，完成句子。

1.The grandchild nods his head to show his ________(同意) to his grandpa.

2.I think __________(回收) can not only protect the environment but also save money.

3.Humans have come to realize the ___________ (重要)of protecting animals.

4.A large population can cause lots of __________ (困难)for the whole nation.

5.There are several chemical factories _______ (倾倒)waste water into the streams.

6.Some parents in less_________(发展) areas prefer boy or girls, don’t they?