根据句意及汉语提示完成句子：

1．His father is a _________（知识渊博的）man．He knows a lot we don't know．

2．We should have the habit of _________（回收利用）the waste things such as wastepaper，bottles，plastic bags and so on．

3．During the long vacation，we are planning to take part in some _________（社会）activities．

4．By end of this _________（世纪），We'll have robots in our house to help us do housework．

5．All the boys were _________（精疲力竭的）after they climbed up to the top of the mountain．