问题
选择题
—I knocked but nobody answered the door.
----They _____asleep then and didn’t hear you.
A.must be
B.should be
C.must have been
D.should have been
答案
答案:C
考察虚拟语气.句意:我敲门但是没有人开门._那时候他们一定是已经睡着了,没有听到你敲门. “must+have+done”表示对过去事情的肯定推测,译成“一定做过某事”故选C.