国家开放大学 / 综合英语（2）
正确率：100%
What a surprise! Bill passed the exam. He _ _ _ _ hard this time.
a.must study
b.should study
c.must have studied
d.may have studied
a.must study
b.should study
c.must have studied
d.may have studied
参考答案：
佳题速递：