第10题: [单项选择]Mary has got a furl mark in the test. She ______ very hard all the time. A. will work B. must have worked C. may work D. could have worked 参考答案:B 答案解析:[解析] must have done表示对过去情况的推测,例如:Her eyes are red. She must have been crying。(她的眼睛红了,一定是哭过了。)D项could