很多考生在英语六级考试阅读部分失分都是因为对句子里面的语法知识不熟悉，看不懂句子的含义。一起随编辑老师通过这篇2014英语六级常考语法精析之情态动词来弥补一下自己的语法缺口吧!
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.