问题补充：
— She looks rather upset. She the exam.
— I guess so. It’s very difficult after all.
A. must have failed
B. can fail
C. would have failed
D. should fail
答案：
A. must have failed
B. can fail
C. would have failed
D. should fail
解析：考查情态动词。句意 她看起来相当沮丧，肯定是考试不及格。我猜是，比较考试太难了。根据上文提到 She looks rather upset 现在看起来沮丧，下文表示对过去的肯定推测must have done ,所以选A项。
考点 :考查情态动词
