1996年1月的 CET-4的第45题是这样的：
I felt somewhat disappointed and was about to leave，______ something occurred which attracted my attention．
A．unlessB．until C．whenD．while
本题从表面上看考核的是状语从句中连词的辨析，但其深层次上考查的却是when的习惯用法中的一种情况：when引导的时间状语从句，表达的意思是："突然，正当那时"。全句意思是："我觉得有些失望，正欲离开，突然发生了一件事吸引了我的注意力。因此，本题答案C。
笔者在辅导四、六级考试时发现，历年四、六级考试中when的习惯用法占有一席之地，为了使同学们进一步掌握when的习惯用法，下面笔者从四个方面，对when的习惯用法作以分析：
1．主句中有过去进行时，be about to do sth．或go on doing sth．等时，从句中用 when，表达的意思是："突然，正当那时"。例如：
I was picking cotton／I was about to go out／I had just stepped out of the door，when it started to pour．
2．与hardly／scarcely．．．when刚……就 常考的是
1）从句中的时态--过去完成时；
2）hardly／scarcely放在句首，用倒装语序。例如：
Scarcely had he gone out when it began to rain heavily．
3．when的省略
1）在when连接的状语从句中，常省略跟主句相同的主语和be动词。其形式为： 连词＋（主语＋be）＋分词／名词／介词短语／形容词。例如：
When（you cross／you are crossing）the street，you should be careful．
2）从句的主谓部分是it is／was（convenient，necessary，possible等）时，it is／was也经常省略。例如：
When（it is）necessary you can help us to do something．
4．when it comes to．．．当提到…… When it comes to mathematics，I am completely at sea．
下面的试题摘自实考试题中，它们有的是显形考题，有的是隐形考题，其中都涉及到了when的用法。同学们不妨试一试：
【真题聚焦】
1．I had just started back for the house to change my clothes ______ I heard voices．
A．as B．whenC．afterD．while（1997／6／44B）
2．The student was just about to ______ the question，when suddenly he found the answer．
A．arrive atB．submit toC．work outD．give up（1995／6／62D）
3．I was halfway back to the cottage where my mother lived ______ Susan caught up with me．
A．whenB．whileC．untilD．though（2001／1／68A）
4． ______ with the size of the whole earth，the highest mountain does not seem high at all．
A．When comparedB．CompareC．While comparingD．Comparing（1990／1／47A）
5．We ______ our breakfast when an old man came to the door．
A．just have hadB．have just hadC．just hadD．had just had（1990／1／53D）
6．I hope my teacher will take my recent illness into ______ when judging my examination．
A．regardB．countingC．accountD．observation（1991／6／52C）
7．Michael used to look hurt and surprised when ______ ．
A．scoldingB．to scoldC．having scoldedD．scolded（1995／1／58D）
8．Doing your homework is a sure way to improve your test scores，and this is especially true ______ it comes to classroom tests．
A．whenB．sinceC．beforeD．after（1996／1／36A）
长春空军第二航空学院/王志英
- 考试辅导
