英语语法归纳与练习

    （一）情态动词

    一。情态动词的现在完成式的用法

    情态动词现在完成式主要有两个功能：表示已经发生的情况和表示虚拟语气。在这两个方面must/mustn't，；can/cann't；need/needn't；may/mayn't；might/mightn't；should/shouldn't；

    ougtht等情态动词＋完成式表示的意思是有一定区别的

    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 __________ apparent the moment I walked into the room， for the first man I met asked sympathetically：“ Are you feeling all right？”

    [A] must be       [B] had been     [C] must have been     [D] had to be

    （答案为C）

    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 __________ my letter； otherwise she would have replied before now.

    [A] couldn't have received     [B] ought to have received

    [C] has received               [D] shouldn't have received

    （答案为A）

    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.

    2.表示虚拟语气。

    1） needn't have + 过去分词，表示做了不必做的事，相当于“didn't need to do”，译为“其实没必要……”。如：

    You needn't have come over yourself.

    As it turned out to be a small house party， we __________ so formally.

    [A] needn't dress up         [B]did not need have dressed up

    [C] did not need dress up     [D] needn't have dressed up

    （没有必要穿的那么正式，体现是说话者的建议，实际结果是否真的穿的很正式没有确定，答案为D）

    2）should have +过去分词，表示应该做某事但实际上未做，译为“本应该……”should not + have过去分词表示本不应该做某事但实际上做了，译为“本不应该……”。如：

    I regret having left the work unfinished； I should have planned everything ahead carefully.

    我本来应该事先认真地把每件事情规划的很好，但实际上作者还是没有规划好，以至工作没有完成。

    3） ought to have +过去分词，表示动作按理该发生了，但实际上未发生，译为“该……”，与should 的完成式含义类似。如：

    Ｔhe porter ought to have called the fire-brigade as soon as he saw the fire in the stock， which went up in smoke .

    4） could have +过去分词，表示过去本来可以做但却未做，译为“完全可以……”。这点与ought/should/ have +过去分词用法相似。如：

    What you said is right， but you could have phrased it more tactfully.

    5） may/ might have +过去分词，表示过去可以做但实际未做，译为“（那样）也许会……”。如：

    It might have been better to include more punchy statistics and photos of equipment in the introduction to further assist first-time office automation managers.