英语四级语法的考查重点（三）

       
        ⑤ 在对名词短语做连词引导时间状语从句时，常与名词构成的其它短语相区别。如：
        You see the lightening ___ it happens, but you hear the thunder later.
        A.the instant B.for an instant C.on the instant D.in an instant
        (1997.1)
        能够引导时间状语从句的是名词the instant，而不是由其构成的介词短语。
       
        ⑥ 注意含有时间状语从句的固定句型，如It won't be long before … 和It is …since两类句型。It won't be long before可以有三个变体，即：It was (not) + 一段时间 + before，It won't be + 一段时间+ before。如95年6月就有对此的考查：
        Scientists say it may be five or ten years ____ it is possible to test this medicine on human patients.
        A.since B.before C.after D.when
       
        2．原因状语从句的连词
        原因状语从句一般由because, since, as, now that, considering that, seeing that连接。对于表原因连词本身的区别考查相对较少，主要是与其它状语从句连词的对比。如：
        ① ____ you are leaving tomorrow, we can eat dinner together tonight.(1999.6)
        A.For B.Since C.Before D.While
       
        ② ____ that my head had cleared, my brain was also beginning to work much better.(1997.6)
        A.For B.Now C.Since D.Despite
       
        1) 从以上两题可以看出，首先，同学们要根据主从句的语意关系，确定是什么状语从句，然后在进行选择。
        2) 注意连词的结构，如2）为Now that的搭配。
        3) 注意for, because, since/as的区别。一般说来，for不表示原因，其所连接的是并列句，是一种解释说明，尤其是当用结果来反证原因时。如：
        He must have experienced something very unpleasant, for he looks so upset.
        You must try to rid yourself of your carelessness, for it often leads to errors.
        4) 注意引导原因状语从句的还可以是considering/seeing that，其用法与since/as相同。如：
        Considering that he is only a beginner, it is understandable for him to make such mistakes.
        Seeing that you have come, you may as well stay here for a few days.
       
        3．条件状语从句的连词
        涉及到条件状语从句的考查题很多，如时态，虚拟语气等。但从状语从句的概念来讲，这里我们所说的是条件状语从句性质的判断和连词的选择。要求同学们首先能理解主从句之间的关系，确定是条件状语从句，然后在根据各连词的特点进行选择。如：
        ① I am sure he is up to the job ____ he would give his mind to it.(1998.1)
        A.if only B.in case C.until D.unless
       
        ② We'll visit Europe next year _____ we have enough money.(1999.1)
        A.lest B.until C.unless D.provided
       
        ③ ____ he works hard, I don't mind when he finishes the experiment.(1998.1)
        A.As soon as B.As well as C.As far as D.So long as
       
        从以上考题来看，就条件状语从句而言，同学们应掌握以下几点：