They must have been here the day before yesterday,__________?A.mustn't they B.didn't they C.mustn't have they D.had they 为什么有yesterday 就要用didn't they?A.为什么不可以呢?
问题描述：
They must have been here the day before yesterday,__________?
A.mustn't they B.didn't they
C.mustn't have they D.had they
为什么有yesterday 就要用didn't they?
A.为什么不可以呢?
答
这里的must表示肯定的猜测,做这类题反意疑问句时需将原句还原为一般句,如此句中为一般过去式(yesterday)所以是did
答
B
答
这里的must表示推测不是一般情态动词的用法,所以要看主句的时态,因为是一般过去时（yesterday）,所以要用助动词didn't