语法总结
过去进行时做背景，一般过去时写短动作
were waiting, were keeping guard 这些长时间动作做背景；arrived, took, opened 这些较短动作切入故事节点。
相似句：
- When I arrived, they were having dinner.
- While she was reading, the phone rang.
过去完成时表示“更早发生”
someone had told the police... 发生在整次机场行动之前，所以用 had told，强调情报早已送达。
相似句：
- He had left before I got there.
- She had finished the work when I called.
steal 与 rob 的区别
steal 后面接被偷的东西，如 steal the diamonds；rob 后面多接人或地点，如 rob a bank, rob a man。
相似句：
- Someone stole my wallet.
- The thieves robbed the bank last night.
to one's surprise 插入评价
To their surprise 用来把叙述者或人物的情绪立即插入句首，特别适合反转情节。
相似句：
- To my surprise, he refused the offer.
- To our surprise, the door was open.