一.because,for,since,as,的区别
because语气强,表示客观必然原因：
He is absent, because he is ill. 因为生病，所以他没来。
比较:He is absent, for he is busy. （“生病”是“缺席”的必然原因，“忙”不是必然原因。）
for 语气轻,表示非客观必然的原因,是主观可改变结果的原因,甚至是猜测可能的原因:
He must be ill, for he is absent. “缺席”不一定是“生病”，只是交流猜测。
for 不能放句首,它是并列连词.
since,as 都是不讲自明的原因,是已知的原因.
Since I am a boy, let me carry the case.
As you don't feel well,you had better stay at home.
1.我不进去了,因为我爸爸在里面. I won't go in .for my father is there.
2.昨晚一定是下雨了,因为地很湿. It must have rained last night,for the ground is web.
3.地是湿的,因为昨晚下雨了. The ground is wet, because it rained last night.
4.因为不高兴,他不想出去了. He diden't wanted to go out,for he was unhappy.
5.既然你工作忙，你就不必跟我们一道去了。 Since/As you are busy, you had better not go with us.
6.他付给我比别人少的钱,因为我是个女的. He paid me less than the others, for I'm female.
7.他付给我比别人少的钱,仅仅因为我是个女的. He paid me less than the others, only because I'm female.
8.既然大家都在这,我们开始开会吧. Since everybody is here,let's begin our meeting.
二.when,while,as引导时间状语时的异同.
when,表示时间点,时间段都可以.如状语是短暂动作时,多用when,是时间段时则三个连词都可以.
When/While/As I was walking in the street,I met a friend of mine.
只能用when 的句型:
1.放句中,主句是进行时,从句是短暂动作,表示这时突然
I was reading in the room, when a girl shouted for help.我正在房间看书，这时突然听到有一个女孩喊救命！
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