根据括号内的汉语提示，完成句子。
小题1:The grandchild nods his head to show his ________(同意) to his grandpa.
小题2:I think __________(回收) can not only protect the environment but also save money.
小题3:Humans have come to realize the ___________ (重要)of protecting animals.
小题4:A large population can cause lots of __________ (困难)for the whole nation.
小题5:There are several chemical factories _______ (倾倒)waste water into the streams.
小题6:Some parents in less_________(发展) areas prefer boy or girls, don’t they?
