原因状语从句

since可用于省略句，而其它不能。如： Since so, there is no more to be said.
关于as
as 引导原因状语从句时表示附带说明的“双方已 知的原因”，语气比since弱，较为正式，位置较 为灵活(常放于主句之前)。
例如： As it is raining, you’d better take a taxi. 既然在下雨， 你最好乘出租汽车。 I went to bed early, as I was exhausted.
(3)because引导的从句可用于强调句，其余不 能。 It’s because he is kind that we like him.
(4)because从句可用作表语，其余不能。 This is because the earth is traveling around the sun.
关于since since引导的原因状语从句一般放于主句之前, 表示已知的、 显然的理由(通常被翻译成“既 然”)， 较为正式,语气比because弱。 例如： Since you are free today, you had better help me with my mathematics. 既然今天你休息， 你最好帮我补习数学。
［考题1］ ____ you’ve got a chance, you might as well make full use of it. A. Now that B. After C. Although D. As soon as ［答案］ A ［解析］ 主句与从句之间存在因果关系， 且 “you’ve got a chance”表示一个显而易 见的原因， 因此应选用表原因的now that。
我睡得早， 因为我筋疲力尽了。
关于for (1)for是并列连词(其他为从属连词)，它有 时可表示因果关系(只能放在主句之后)是 对前面分句的内容加以解释。如： It rained last night, for the ground is wet this morning.
(2)for“因为,由于”表明附加或推断的理 由，引导的分句前常有逗号。for分句不放 句首.是用来附带解释或说明前一分句的原 因和理由。例如： Day breaks, for the bird sings.
Adverbial Clause of Reason
原因状语wk.baidu.com句
Conjunctions： because , since , as , for , now that
关于because (1)because表示的原因是必然的因果关系，语气 最强，通常放在主句之后，有时也放在主句之前。 You want to know why I am leaving? I am leaving because I am fed up. (2)回答why提出的问题，只能用because, 不能用 其余三者。 A：Why can’t I go? B：Because you are too young.
关于now that now that用来说明一种新情况，然后加以推论。 常和since互换。 • Now that you are ready, we'll start at once. 既然你已经准备好了，我们马上开始。
注意：汉语习惯上说“因为„„所以”， 但英语却不能将because, since, as, for等与 so(所以)连用。
［考题2］ He found it increasingly difficult to read, ____ his eyesight was beginning to fail. (2006北京) A. and B. for C. but D. or ［答案］ B ［解析］ “his eyesight was beginning to fail” 是“he found it increasingly difficult to read”的原因， 因此本题应选用可以表示原因 的连词for引导原因状语从句。
［考题3］——Why were you absent from the meeting last night? • ——____ I had to deal with some urgent things. • A. Because B. For C.Now that D.As ［答案］ A ［解析］ 回答why的提问，用because。