句型13
…until…."直到……时候";not…until…"直到……才……"
[例句]
You are to stay until/till your mother comes back. 你得等到你妈妈回来。
The meeting was put off until ten o'clock. 会议推迟到十点钟。
The villagers didn't realize how serious the pollution was until all the fish died in the river.
→Not until all the fish died in the river did the villagers realize how serious the pollution was.(倒装句)
等到湖里的鱼全死光了，村民们才意识到污染是多么严重。
He didn't go to bed until his mother came back.
→It was not until his mother came back that he went to bed.(强调句)
Not until he failed in the exam did he realize that he had wasted much time playing computer games.
Not until his son came back from school did he go to bed.
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。
