Question

--- He worked out such different questions at a very young age.
--- Oh, he ______ a very smart student then.

A．could have been	B．should have been
C．might have been	D．must have been

Answer 1

D

试题分析：句意：--在这么小的年龄他就能提出不同的问题。--哦，那他当时一定是非常聪明的。could have done过去本可以做某事而未做成； should have done 指过去应该做某事而实际未做；might have done 表示过去可能做某事；must have done表示过去一定能做某事。根据then可知这是指at a very young age，所以表示动作已经过去了，根据第一句可知这里推测的可能性很大，故选D。
点评：本题难度适中。情态动词是高中阶段的重难点之一，需要考生熟记它们的用法，在各类考试中经常出现，情态动词的完成式主要用于表示对过去情况进行推测或责备也是高考常考的内容。
即学即练：I didn’t see her in the meeting-room this morning. She ____ at the meeting.
A. mustn’t have spoken    B. shouldn’t have spoken
C. needn’t have spoken    D. couldn’t have spoken
解析：D。本句表达的是过去已发生情况否定的推测判断，应该用couldn’t have done.