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上次，我们学习了如何“退一步”，也即让步状语从句的知识考点。今天，小编打算分享一个新东西，帮大家理清楚世事的来龙去脉。它就是我们的——原因状语从句。其实呢，这世上的事情并不复杂，只需搞懂它的因为+所以，种种疑难杂症便会不攻自破！好啦，废话不多说，我们快来开启原因状语从句之门吧！(☄⊙ω⊙)☄ 一、because, since/now that, as的用法区别：考点1：because引导的原因状语从句可位于句首、句中。because表直接原因，语气最强，回答why引导的疑问句。I didn't go because I was afraid.I can't get to sleep because there is too much noise outside.We went by bus because it was cheaper.注意：because不能与so连用。I do it because I like it. = I like it so I do it. （）Because I like it so I do it. （）He can't go to school because he is ill.= He is ill so he can't go to school.（）Because he is ill so he can't go to school. （）考点2：since引导的原因状语从句一般放于主句之前，表示双方已知的、 显然的理由，(翻译成“既然”= now that )，语气比because弱。Since he has a car now, it is much easier for him to go out.Since you are free today, can you help me with my work?Now that you are an adult, you should rely on yourself.Now that she was indoors, she had not been wearing a coat.考点3：as引导原因状从一般放在句首，表示附带说明的“双方已知的原因”，含有对比说明的意味，语气比since弱。As he is still a young boy, you may forgive him.As you are tired, you had better have a rest.I went to bed early, as I was tired yesterday.考点4：for引导的并列句只能放于句中，必须用逗号隔开，语气最弱，用来表推测。It must have rained last night, for the road is wet.He could not have seen me, for I was not there.He seldom goes out now, for he is very old.二．when也可以引导原因状语从句，表示“既然”。I won't tell you when you won't listen.It was foolish of you to take a taxi when you could easily walk there in five minutes.小编寄语：1). 回答why引导的疑问句用because，但不能与so连用；2). for引导的并列句只能放于句中，并用逗号隔开；3). when也可以引导原因状语从句，表示“既然”。

--摘自：百词斩