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。
“俊狼猎英”团队为您解答 不懂欢迎追问
追问能不能说的具体点？我就想知道当when引导从句时主句与从句的时态。
追答时间状语的时态是不确定的，不过when 引导的，最常见的就是主句是一般过去时，从句用过去进行时···
翻译就是：当....时，另外一个事情正在发生
如：When I was fishing， it began to rain 开始下雨的时候，我正在钓鱼