句型14

unless…"除非，如果不……"(=if…not)

[例句]

I shall go tomorrow unless it rains. 如果不下雨，我明天去。

-Shall Tom go and play football?

-Not unless he has finished his homework. 除非他完成作业，否则不能出去。

I won't go unless he comes to invite me himself.

除非他本人来邀请我，不然我是不会去的。

I won't attend his birthday party unless invited (=unless I am invited). 除非被邀请，否则我不

去参加的生日晚会。

句型15

when引导的从句

when除了用来引导主语从句、宾语从句、时间状语从句、表语从句和定语从句，还有一种用法值得关注，那就是when引导并列分句，意思是"这 时突然;就在那时"，强调另一个动作的突然发生。常用于以下句型中：(1)、主语 + be doing… when…意思是"正在做某事这时……";(2)、主语 + be about to do…when…;(3)、主语+be on the point of (doing) …when…意思是"正要去做某事这时……"

[例句]

One day Chuck was on a flight across the Pacific Ocean when suddenly his plane crashed. 有一天，Chuck正在太平洋上飞行，这时他的飞机突然爆炸了。

I don't know when he will arrive. 我不晓得他什么时候到达。

I thought of the happy days when I was in Beijing. 我想起了在北京时的那段快乐日子。

I believe the time will soon come when there will be no weapons in the world. 我相信世界上没有武器的日子不久就会到来。

I was walking along the river when I heard a drowning boy cry for help. 我正在河边行走，这时我突然听到一个落水男孩求救。

I was about to leave when it began to rain. 我刚要离开，这时下雨了。

I had just finished my exam paper when the bell rang, announcing the class was over. 我刚做完作业，下课铃响了。

I thought of the happy days when I was in France. 我想到了在法国时那段快乐日子。

I believe the time will soon come when there will be no weapons in the world. 我相信世界上没有武器的日子不久就会来临。

[比较]

I was walking along the street when I caught sight of a tailor's shop. 我正在街上走，这时我看见一家裁缝店。

I was walking along the streets. Just at the moment I caught sight of a tailor's shop. 我在街上走。就在那时我看见一家裁缝店。