重点讲解：
1. serve as 用作；可当…使用；充作；
The sofa will serve as a bed for a night or two.
沙发可以当床凑合一两夜L2t*Y=y|j.HrK。
2. quench one's thirst 解(渴)；止(渴)；
He stopped to quench his thirst at a stream.
他停了下来，在小溪边饮水止渴qa2bQf=j+,B@7m0W。
3. hint at 暗示；示意；
A character's appearance may hint at her past.
一名角色的形象可能暗示其过去的经历9Bd2hR)paBdBvMp@|P。
4. by accident 意外；偶然；
She discovered the problem by accident.
她碰巧发现了这个问题qv~sQSl@Zsg&C3h。