摘要：3．在强调结构It is/was-that和关联词not-but 引导的原因状语从句中.宜用because. It's because he helped you that I'm prepared to help him. 正是因为他帮助过你.所以我乐意去帮助他. He decided to give up the chance of going abroad, not because he did not want to but because his wife was ill. 他决定放弃出国的机会.不是因为他不想去.而是因为他妻子病了. B． since since 因为.既然.引导的从句大多置于句首.主从句的时态一般相同. Since you have no license, you are not allowed to drive. 因为你没有驾驶执照.所以不允许你开车. Since you are al here, let's try and reach a decision. 既然大家都来了.咱们就设法做出一个决定吧. C．as as 由于.一般多用于句首. As she was ill, she didn't come to the party. 由于病了.她没来参加晚会. As he was not well enough, I had to go without him. 由于他身体欠佳.我只好不带他去了. As it rained, we all stayed at home. 由于下雨我们都呆在家里. C． because, since, as 的区别

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