重点讲解：
1.a couple of days 几天
例句：He stayed in London for a couple of days.
他在伦敦呆了几天。

2.be exposed to 暴露在
例句：It sounds reasonable that when someone runs up and down , the body is exposed to more drops of water .
这听起来似乎不无道理，因为人们在跑动时，身体暴露得多，淋到的雨也多。

3.be warm with ...的需求
例句：It was really windy, and we kept telling him it would be warm with three people in the tent.
晚上风很大，而且我们一个劲儿的告诉他三个人在帐篷里一定会很暖和。

4.on a diet of 以。。为食
例句：The Irish used to live on a diet of potatoes.
爱尔兰人过去用马铃薯作为主食。