John’s score on the test is the highest in the class; he

John’s score on the test is the highest in the class; he _____ last night.

must study

should have studied

must have studied

is sure to study

答案及解析：本题考查情态动词C选项，句意：约翰的考试分数全班最高;他昨天晚上一定学习了。表示对过去某一动作行为的猜测须要用must have done这一句型结构。A，选项，对现在的猜测，与题意不符，故排除。B，选项，本该做而未做，故排除。D，与题意不符，故排除。故正确答案为C选项。