【题目】— John graduated from college at a very young age.
— Oh, he _________a very smart boy then.
A.could have beenB.must have beenC.should beD.might be
在线课程【答案】B
【解析】
考查情态动词+have done。句意：---约翰很年轻就从大学毕业了。---哦，那他一定是个很聪明的孩子。根据“ John graduated from college at a very young age.”可知，must have been表示对过去肯定的猜测，“过去一定做了某事”。故选B项。