重点讲解：
1. in the middle of (某件事或某段时间的)中期；
例句：She came in the middle of the day.
她在中午的时候来了。
2. wait on 服务；服侍；招待；
例句：There were plenty of servants to wait on her.
有很多仆人服侍她。
3. fall out (头发、牙齿)掉落，脱落；
例句：Her hair started falling out as a result of radiation treatment.
由于放疗，她开始掉头发。
4. be afraid of 害怕的；恐惧的；
例句：Some children are afraid of the dark.
有些小孩怕黑。
