语法点：时间状语从句 when / while / as soon as / before / after (Time Clauses)
时间状语从句告诉我们主句动作"什么时候"发生，由 when（当……时）、while（在……期间，多接进行时）、as soon as（一……就）、before（在……之前）、after（在……之后）等连词引导。从句可以放在句首（后面加逗号）或句尾。讲过去的故事时，主从句都用一般过去时；如果从句动作明显早于主句，也可以用过去完成时。本课讲飞机失事后一位母亲如何求救，作者用 When … flew off course、When it grew dark、It was not long before … 把事件按时间串起来。
结构
| 连词 | 含义 | 例句 |
|---|---|---|
| when | 当……时 | When it grew dark, she turned a suitcase into a bed. |
| while | 在……期间 | While she was waiting, she heard planes overhead. |
| as soon as | 一……就 | As soon as the pilot saw the signal, he sent a message. |
| before | 在……之前 | It was not long before a helicopter arrived. |
| after | 在……之后 | After the plane crashed, the woman looked for shelter. |
要点：1) 从句在前用逗号，在后不用；2) 讲将来的事时，从句用一般现在时代替将来时（When it gets dark, we will stop.）；3) while 后多用进行时，when 多用一般时。
课文中的例句
- [句 1] When a light passenger plane flew off course some time ago, it crashed in the mountains… — when 从句在句首，主从句都用一般过去时
- [句 6] When it grew dark, she turned a suitcase into a bed… — when + 天色变化，引出主句动作
- [句 7] During the night, it got terribly cold. — 介词短语 during the night 也可表时间，与从句对比
- [句 12] It was not long before a helicopter arrived on the scene… — It was not long before 意为"不久……就"
- [句 9] Early next morning, she heard planes passing overhead… — 时间状语 + 一般过去时，与从句形式对照
补充例句
- As soon as the plane crashed, the woman looked after her daughters. — 飞机一坠毁，那位妇女就照顾起她的女儿们。
- While the children were sleeping, she stamped out 'SOS' in the snow. — 孩子们睡觉的时候，她在雪地上踩出了 SOS。
- After the pilot saw the signal, he sent a message by radio. — 飞行员看到信号后，用无线电发了消息。
易错点
- ❌ When it will grow dark, we will stop. → ✅ When it grows dark, we will stop. — 时间从句里不用 will，用一般现在时表将来。
- ❌ She heard planes, when she woke up. → ✅ She heard planes when she woke up. — 从句放在句尾时不加逗号。
- ❌ As soon as the pilot saw the signal, he sends a message. → ✅ As soon as the pilot saw the signal, he sent a message. — 主从句时态要一致，都用过去时。
- ❌ It was not long that a helicopter arrived. → ✅ It was not long before a helicopter arrived. — 固定句型 It was not long before …。