when引導(dǎo)的從句
　　when除了用來引導(dǎo)主語從句、賓語從句、時(shí)間狀語從句、表語從句和定語從句，還有一種用法值得關(guān)注，那就是when引導(dǎo)并列分句，意思是“這時(shí)突然;就在那時(shí)”，強(qiáng)調(diào)另一個(gè)動(dòng)作的突然發(fā)生。常用于以下句型中：(1)、主語 + be doing… when…意思是“正在做某事這時(shí)……”;(2)、主語 + be about to do…when…;(3)、主語+be on the point of (doing) …when…意思是“正要去做某事這時(shí)……”
　　[例句]
　　One day Chuck was on a flight across the Pacific Ocean when suddenly his plane crashed. 有一天，Chuck正在太平洋上飛行，這時(shí)他的飛機(jī)突然爆炸了。
　　I don’t know when he will arrive. 我不曉得他什么時(shí)候到達(dá)。
　　I thought of the happy days when I was in Beijing. 我想起了在北京時(shí)的那段快樂日子。
　　I believe the time will soon come when there will be no weapons in the world. 我相信世界上沒有武器的日子不久就會(huì)到來。
　　I was walking along the river when I heard a drowning boy cry for help. 我正在河邊行走，這時(shí)我突然聽到一個(gè)落水男孩求救。
　　I was about to leave when it began to rain. 我剛要離開，這時(shí)下雨了。
　　I had just finished my exam paper when the bell rang, announcing the class was over. 我剛做完作業(yè)，下課鈴響了。
　　I thought of the happy days when I was in France. 我想到了在法國時(shí)那段快樂日子。
　　I believe the time will soon come when there will be no weapons in the world. 我相信世界上沒有武器的日子不久就會(huì)來臨。
　　[比較]
　　I was walking along the street when I caught sight of a tailor’s shop. 我正在街上走，這時(shí)我看見一家裁縫店。
　　I was walking along the streets. Just at the moment I caught sight of a tailor’s shop. 我在街上走。就在那時(shí)我看見一家裁縫店。