Question

初中英语问题

I didn't hear the phone . I ___ slepping then . ( ) A.must been B.must have been C.should be D.should have been 好需要理由!

Answer 1

B
情态动词表示肯定的判断用must，A显然错误，所以选B

Answer 2

since在这里是副词
=
since
then
原句完全正确。
since后面跟句子
时
是从属连词
since后面跟名词或短语时
是
介词
since什么后面什么也没有
是副词