once的意思是“一旦”，对于涉及once的考题，一般只要能读懂句意，弄清语境，一般不会有问题。如：

1. You will be successful in the interview ______ you have confidence. (福建卷)

A. before　　　 　　 B. once　 C. until D. though

until的意思是“直到……时”“在……之前”，对于涉及until的考题，一般只要能读懂句意，弄清语境，一般不会有问题。如：

It is difficult for us to learn a lesson in life ___A___ we’ve actually had that lesson. (天津卷)

A. until　 B. after C. since　　　 D. when

另外，还要注意not…until…这一句式(直到……才)。如：

“You can’t have this football back ___D___ you promise not to kick it at my cat again,” the old man said firmly. (广东卷)

A. because　　 B. since　　　 C. when　　　 D. until

2. I won’t call you, ______ something unexpected happens. (全国I)

A. unless　　　 B. whether　 C. because　 D. while

[解析]两道题都选unless，均表示“除非”。

unless的意思是“如果不……”“除非”，对于涉及unless的考题，一般只要能读懂句意，弄清语境，一般不会有问题。如：

1. Most birds find it safe to sleep in the trees, but ______ they have eggs or young chicks, they don’t use a nest. (湖南卷)

A. why　 B. how C. unless　　　 　　 D. where

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

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

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

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……”。

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. 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”。