20.5 表原因關(guān)系
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1) for
判斷改錯(cuò)：
　 (錯(cuò)) For he is ill, he is absent today.
　 (對(duì)) He is absent today, for he is ill.
　 for是并列連詞，不能置于含兩個(gè)并列分句的句子的句首，只能將其放在兩個(gè)分句中間。

2) so, therefore
　　He hurt his leg, so he couldn't play in the game.

注意：
　 a. 兩個(gè)并列連詞不能連用，但therefore, then, yet.可以和并列連詞連用。
　　　You can watch TV, and or you can go to bed.
　　　He hurt his leg, and so / and therefore he couldn't play in the game.

　 b. although… yet…，但although不與 but連用。
　　 (錯(cuò))　Although he was weak, but he tried his best to do the work..
　　 (對(duì))　Although he was weak, yet he tried his best to do the work.