试一试: Amina 想解释她为什么待在家。原因是下雨。 哪个说明了原因？ (I stayed home because it was raining. / I stayed home so it was raining.) 答案: I stayed home because it was raining. — 她在说明原因（为什么待在家），所以用 because：because it was raining。"So it was raining" 会让人以为下雨是待在家的结果，这说不通。
试一试: Hiroshi 想说他因此做了什么。先下了雨，待在家是接下来发生的事。 哪个说明了结果？ (It was raining, so I stayed home. / It was raining, because I stayed home.) 答案: It was raining, so I stayed home. — 他在说明结果（接下来做了什么），所以用 so：so I stayed home。"Because I stayed home" 会说成下雨是因为他待在家，这就反过来了。
although 表示意外
后半句的内容出乎意料、跟前半句不搭时，用 although 表示意外。它可以放在句首（后面加逗号），也可以放在句中连接（不加逗号）。
Although it was raining, we went out. (surprising, you'd expect us to stay in)
She passed although she didn't study.
Although the hotel was expensive, we enjoyed it.
试一试: 天气不好，你会以为大家都待在屋里。可 Mei 和朋友们还是出门了。这出人意料。 哪个表示了意外？ (Although it was raining, they went out. / Because it was raining, they went out.) 答案: Although it was raining, they went out. — 在雨天出门是出人意料的，所以用 although：Although it was raining, they went out。"Because it was raining" 会说成下雨是他们出门的原因，而不是意外。
but 表示转折
用 but 连接两个不一样或出人意料的想法。But 放在句子中间，前面通常有逗号。它跟 although 一样表示转折——不过 although 可以放在句首，but 只能在中间连接。
It was raining, but we went out.
The hotel was expensive, but we enjoyed it.
I was tired, but I finished my work.
Not "But it was raining, we went out." — say "It was raining, but we went out.". But 只在句子中间连接；它不能像 although 那样放在句首。
试一试: 房间很小。你可能会觉得这是个缺点。但它却很舒适。这两个想法是不一样的。 哪个表示了转折？ (The room was small, but it was comfortable. / The room was small, so it was comfortable.) 答案: The room was small, but it was comfortable. — 这两个想法不一样（小，却舒适），所以用 but 表示转折：small, but comfortable。"So it was comfortable" 会说成因为小所以舒适，这不是句子的本意。
只用一个连接词
只选一个连接词，不要选两个。不要把 because ... so 一起用，也不要把 although ... but 一起用。
Because it rained, we stayed home. (not "Because it rained, so we stayed")
Although I was tired, I went out. (not "Although I was tired, but I went out")
Not "Although I was tired, but I went out." — say "Although I was tired, I went out.". Although 本身已经表示了意外，所以不需要再加 but。
试一试: Which one is right? (Because it was late, we went home. / Because it was late, so we went home. / Although it was late, but we went home.) 答案: Because it was late, we went home. — 一个连接词就够了：Because it was late, we went home。"Because ... so" 和 "Although ... but" 都重复用了两个连接词，其实只需要一个。