初二英语用恰当的介词填空怎么做?（方法+理由）

初二英语用恰当的介词填空怎么做?（方法+理由）
例题：1、What are they doing _____ the coming vacation?
2、My uncle is going hiking _____ the mountains this Friday.
3、My best friend sent me these photos_____ Hong Kong.
4、I'll show you how to do it when I get back _____ school from San Francisco.
5、Cathy's father is going to Hawaii _____ December 4th.