一、in case引导的状语从句
根据语境的不同，in case既可表示“如果”“万一”，引导条件状语从句;也可表示“以防(万一)”，引导目的状语从句。下面两道真题均选in case：
1. Leave your key with a neighbor ______ you lock yourself out one day. (北京卷)
A. ever since B. even if C. soon after D. in case
2. My parents live in a small village. They always keep candles in the house ______ there is a power cut. (重庆卷)
A. if B. unless C. in case D. so that
【解析】两道题都选in case，均表示“以防万一”。
二、before引导的状语从句
尤其要注意“it+be+一段时间+before…”这一句型。如：
1. The field research will take Joan and Paul about five months; it will be a long time ______ we meet them again. (安徽卷)
A. after B. before C. since D. when
2. He was told that it would be at least three more months ______ he could recover and return to work. (江西卷)
A. when B. before C. since D. that
【解析】两道题均before。第1题涉及的句式为：It will be a long time before…，意思是“要过很久才会……”;第2题涉及的句式为：it was some time before…，意思是“在……之前过了一段时间”，通常可转译为“要过一段时间才会……”。
三、while引导的状语从句
尤其要注意while表示“尽管”“虽然”时的用法(此时它引导的不是时间状语从句，而是让步状语从句——此用法许多同学并不熟悉，值得特别注意!)。如：
______ I really don’t like art I find his work impressive. (山东卷)
A. As B. Since C. If D. While
【解析】答案选D。while在此表示“尽管”“虽然”，又如：While the work was difficult it was interesting. 尽管工作有难度，但很有趣。/While I understand what you say I can’t agree with you. 虽然我理解你的意思，但我还是不同意。
另外，while表示对比的用法也值得注意(此时它表示“而”)。如：
The cost of living in Glasgow is among the lowest in Britain ______ the quality of life is probably one of the highest. (天津卷)
A. since B. when C. as D. while
四、when引导的状语从句
对于when的用法，同学们最熟悉的是表示“当……的时候”。如：
—Where’s that report?
—I brought it to you ______ you were in Mr. Black’s office yesterday. (北京卷)
A. if B. when C. because D. before
【解析】答案选B。将四个选项逐一填入空格处，只有填when时，意思最通顺。句意为：当你昨天在布莱克先生办公室时我就带给你了。
但是when还有一个用法，就是表示“既然”。如：
Why do you want a new job ___D___ you’ve got such a good one already?
A. that B. where C. which D. when
还有一点也需注意，就是when表示“这时(突然)”的用法。如：
1. I had just stepped out of the bathroom and was busily drying myself with a towel ___B___ I heard the steps. (湖南卷)
A. while B. when C. since D. after
2. He was about halfway through his meal ___C___ a familiar voice came to his ears. (辽宁卷)
A. why B. where C. when D. while
