重点讲解：
1. in a word 总而言之；简言之；一句话；
例句：In a word, the situation is serious.
总而言之，形势很严峻。
2. do sb. a favor 恩惠；帮忙；
例句：He is always ready to do his classmates a favor.
他总是乐于帮助同学。
3. stop doing sth. 停止；停下；
例句：I stopped working last year to have a baby.
我去年因生小孩辞去了工作。
4. require sb. to do sth./sb. be required to do sth. 要求；命令；规定；
例句：The rules also require employers to provide safety training.
这些规定还要求雇主提供安全培训。