1.A
2.B
3.C
4.C
5.C
6.C
7.A
8.D
9.A
10.C
比较：because,since,as和for
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.
希望可以帮你!