—When I first got to Harvard, my awkward English brought me great trouble.
——Oh, dear, it a struggle for you to keep up with other students.
A. might be
B. can be
C. could have been
D. must have been
网友回答
A. might be
B. can be
C. could have been
(答案→)D. must have been
解析：考查情态动词+have done的用法：句意：--当我第一次到哈佛，我蹩脚的英语给我带来很多麻烦。--哦，那你要跟上其他同学一定很难。可知是对过去的推测，用情态动词+have done，could have been过去可能做却没做， must have been过去一定做了。选D。