2012考研必备：考研英语语法精要(21)

考研网

七、情态动词
    注意情态动词完成式的用法有两方面的含义：
   
    1.表示已经发生的情况
    (1)must have +过去分词，表示对已发生情况的肯定推测，译为“(昨天)一定……”。如：
    My pain must have been apparent the moment I walked into the room, for the first man I met asked sympathetically: “Are you feeling all right?”
    (2)cant/couldn’t have +过去分词，表示对已发生情况的否定推测，译为“(昨天)一定没……”。 如：
    Mary couldn’t have received my letter; otherwise she would have replied before now.
    (3)may/might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，或事实上根本没发生，译为“也许……”。如：
    At Florida Power’s Crystal River plant, a potentially serious leakage of radioactive water may have been unknowingly caused by an electrician.