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。

　　句型16
　　while引导的从句
　　while除了有"当/在……时候"的意思外(注意：引导的句子谓语动词只能是延续性动词!)，另外的两层意思也是考查的重点： (1)while = although "尽管"、"虽然"，引导让步状语从句;(2)while的意思是"然而;可是"，常用来表达对比关系。
　　[例句]
　　While I admit that the problem is difficult, I don't think that they can't be solved.
　　尽管我承认这个问题很难，但是我并不认为无法解决。
　　While I admit his good points, I can see his shortcomings.
　　虽然我承认他的优点，我也能看出他的缺点。
　　While I was angry with her, I didn't lose my temper.
　　虽然我很生气，但我当时没有对她发脾气。
　　While I understand your viewpoint, I don't agree with you. 虽然我了解你的见解， 我还是不能同意(你)。
　　I earn only 120 dollars a week, while she earns 180 dollars. 我一星期只赚120美元，她却赚180美元。

　　句型17
　　where…(地点从句)
　　[注意]where引导地点从句时，可以引导定语从句或是逻辑地点状语从句。当它在定语从句中作地点状语，指代地点时，这时可以用in which, on which, at which, to which, from which等结构代替。但是它引导逻辑地点状语从句时，没有这样用法。
　　[例句]
　　You should put the book where it was. 把书放回原处。
　　Persistent people begin their success where others end in failure.
　　不屈不挠者从他人失败的地方获取成功。
　　Where there is a will, there is a way. 有志者，事竟成。
　　Where men are greedy, there is never peace. 人类贪欲不止，世界和平无望。
　　Go where you should, keep on studying. 无论你到哪里，你都应该继续学习。
　　That is the building where my father works. 那是我父亲工作的大楼。
　　Yesterday I went to the department store, where I met my teacher. 昨天我去百货公司，就在那儿遇见了我的老师。
　　That's where a change is needed. 那就是需要变更的地方。
　　We could see the runners very well from where we stood. 从我们所站的地方能很清楚地看到赛跑的选手。
　　You should let your children play where you can see them. 你应该让小孩在你的视线所及的地方玩耍。
　　Potatoes can be grown in places where it is too cold to grow rice.=Potatoes can be grown in places where it is too cold to grow rice.(本句where引导定语从句)
　　有些地方太冷不能种水稻，但可以种马铃薯。
　　[请比较下面的句子结构的不同]
　　Potatoes can be grown where it is too cold to grow rice.(本句where引导地点状语从句)