when的用法

when的句子结构常用于以下句型中：(1)主语+bedoing…when(suddenly)…意思是“正在做某事这时(突然)……”;(2)主语+beabouttodo…when…;主语+beonthepointof(doing)…when…意思是“正要去做某事这时……”(3)主语+hadjustdone…when...某人刚做完某事时突然...(4)主语+hadhardly/scarcely/barelydone…when…Hardly/Scarcely/Barelyhad+主语+done…when…一…就…IwaswalkingalongtheriverwhensuddenlyIheardadrowningboycryforhelp.我正在河边行走,这时我突然听到一个落水男孩求救.Iwasabouttoleavewhenitbegantorain.我正要离开,这时下雨了.Ihadjustfinishedmyexampaperwhenthebellrang,announcingtheclasswasover.我刚做完试卷,下课铃响了.Ihadhardlygottothebusstopwhenthebusstarted.我一到公共汽车站，汽车就开了。HardlyhadIgottothebusstopwhenthebusstarted.nosooner…than…Ihadnosoonergottothebusstopthanthebusstarted.NosoonerhadIgottothebusstopthanthebusstarted.AssoonasIgottothebusstop,thebusstarted.他一回来就买了一套房子。（nosooner…than…）Hehadnosoonerreturnedthanheboughtahouse.Nosoonerhadhereturnedthanheboughtahouse.Themoment,tneminute,thesecond,theinstanton(doing)…Immediately,instantly