表原因连词的用法及区别for as since because whilenow that

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表原因连词的用法及区别for as since because whilenow that

表原因连词的用法及区别for as since because whilenow that
表原因连词的用法及区别
for as since because while
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表原因连词的用法及区别for as since because whilenow that
1) because语势最强,用来说明人所不知的原因,回答why提出的问题,是句子中的重要部分,常放在句末,不能用其它三个替换.逗号可加可不加.
You can trust those products because the quality never changes.
I haven”t been to the cinema lately,because I am too busy.
I didn”t go,because I was afraid.
2)当原因是显而易见的或已为人们所知,就用as或 since.since稍正式一些.
Since /As the weather is so bad,we have to delay our journey.
3) 由because引导的从句如果放在句末,且前面有逗 号,则可以用for来代替.但如果不是说明直接原因,而是多种情况加以推断,就只能用for.
He is absent today,because / for he is ill.
He must be ill,for he is absent today.
4)当because引导的从句与否定的主句连用,而主句又位于句首时,之前不用逗号,因为主句动词否定的是其后的全部内容.为了突出because从句,because 前常加上副词,如:just,only,simply,chiefly等.在这种情况下,常常会形成否定的转移.如果是在口语中,在because前要有一个停顿(逗号),才能表示出否定没有转到because从句中.如:
You should not despise a man just because he is poorly dressed.
She is not marrying Bill,because he is poor.
because引导的从句可以被just,only,simply等副词修饰,也可以用并列连词构成并列的 because从句,而since和as则不能.如:We pardoned him only because he was still young.for表示原因时,置于主句之后,表示非直接的随后附加说明的理由或推断理由.如:She didn’t go to school,for she was ill.