试题题干
— Mary looks very upset. She（ ）failed to pass the exam.
— I guess so. It's very difficult after all.
参考答案
正确答案：
试题解析
本题考查情态动词的用法。must have done一定做了某事；could have done本可以做某事；should have done sth本应该做某事；might have done也许做了某事。结合句意可知A正确。
句意：—— 玛丽看起来很难过。她一定考试没有及格。—— 我想是的。毕竟考试很难。