英语四级语法的考查重点（一）

        C. will be rising D. has been rising
       
        3) 而现在完成时表示到目前为止某个动作已经结束，对现在有影响，如4）。从下文中的"正在修改"可以判断人们已经对牛顿的观点提出挑战，而不是将要提出挑战或者可能提出挑战，由此可以判断应该用现在完成时。
       
        4) 与现在完成时不同，现在完成进行时则表示某个动作从过去持续到现在，并且仍在进行，如2）。头疼的原因是看书时间太长。本题可以用现在完成时，但不会是过去完成时，选项B不对，一般现在时表示经常发生的动作，与这里的头疼不能构成直接的因果关系，由于时间状语表示的是一段时间，有不可能是现在进行时，所以这里只能用现在完成进行时。
       
        C．完成时态使用注意事项
        ① 完成时的时间状语一般表示"到……为止"，以"by"短语居多。如果句中的时间状语是由by引出的短语或从句，谓语动词一般是用完成时态，如：
        By the time we got there, the fire had already been put out.
        We'll have completed the task by the time you come back.
       
        ② 在完成时态中，终止性动词不能与表示一段时间的时间状语连用，而表示状态或动作持续的谓语动词必须与表示一段时间的状语连用。
        The conference ____ a full week by the time it ends
        A. must have lasted B. will have lasted
        C. would last D. has lasted (1997.1)
        It seems oil ___ form this pipe for some time. We'll have to take the machine apart to put it right.
        A. had leaked B. is leaking C. leaked D. has been leaking (1997.6)
        这两题中都有表示动作持续的一段时间，应该用完成时态。
        但是，如果只表示状态已经存在，则不能用完成时态，如：
        By then, he knew what he waned to be when he grew up.
       
        ③ 完成时可以用来表示量的积累。
       
        ④ 对于完成时的考查有两种，一种是时态本身的选择，另一种是根据时态选择时间状语，如6）。从句时态为过去完成时，表示等到他回来，客人都已经离开了，与完成时态连用的，表示"到……为止"的应该是介词by。
        Pactise Yourself
        下面请同学们做《语法分册》第五章 二至四节相关题目。然后对照评析自检。
       
        Test Yourself
        刚才我们看了完成时态的考查，现在我们一块来看以下其它时态，请先试做以下各题：
        1) Turn on the television or open a magazine and you _____ advertisements showing happy, balanced families.
        A. are often seeing B. often see C. will often see D. have often seen (1995.6)
       
        2) While people may refer to television for up-to-the-minute news, it is unlikely that television _____ the newspaper completely.
        A. replaced B. have replaced C. replace D. will replace (1995.6)
       
        3) I'm sorry I can't see you immediately; but if you'd like to take a seat, I'll be with you ____.
        A. for a moment B. in a moment C. for the moment D. at the moment (1999.1)
       
        4) If she doesn't tell him the truth now, he'll simply keep on asking her until she _____.