原因状语从句
表示「因为」，because 与 so 不能连用。
because / since / as + 从句
要点
- because 表示直接原因，语气最强。
- since 表示「既然」，语气较弱，常放在句首。
- as 表示原因时语气最弱。
- ⚠️ because 与 so 不能出现在同一个句子里。
- now that 说的是双方都知道的既成情况："既然眼下…" —— 它不解释为什么，只摆出"如今是这样"，所以语气比 because 软。
- for 也能表原因，但它是并列连词：只跟在主句后面、前面有停顿，也不能拿来回答 Why。He said little, for he was tired.
- thanks to（多亏，也能反着说）与 owing to（由于，书面）后面接的是名词短语：Thanks to the early bus, we had ten minutes left.
例句
I like math because it is fun.
我喜欢数学因为它很有趣。
Because they are cute.
因为它们很可爱。
Sharks are endangered because of human activities.
鲨鱼因人类活动而濒危。
They had to call off the match because of the rain.
因为下雨，比赛只好取消了。
Now that the rain has stopped, we can go out.
雨既然停了，我们就能出去。
He put down the letter, for his hands were shaking.
他放下了那封信，因为手在抖。
易错提示
- because 后面接句子，because of 后面接名词短语。
- because 和 so 只能留一个，中文的「因为……所以……」英文不成立。
- the reason why … is because 这一式被看成重复，写成 The reason why he left is that he was ill. 更稳 —— is 后面该站名词性的 that 从句。