when的时态用法When的从句的时态可以有哪些?还有主句的时态可以任意吗?.比如刚做到这一题They had just reached the middle when there came a great shout behind them.这一句应该用when 可是从句是过去时 主句

when的时态用法When的从句的时态可以有哪些?还有主句的时态可以任意吗?.比如刚做到这一题They had just reached the middle when there came a great shout behind them.这一句应该用when 可是从句是过去时 主句
when的时态用法
When的从句的时态可以有哪些?
还有主句的时态可以任意吗?.
比如刚做到这一题
They had just reached the middle when there came a great shout behind them.
这一句应该用when 可是从句是过去时 主句可以是过去完成时吗?

when的时态用法When的从句的时态可以有哪些?还有主句的时态可以任意吗?.比如刚做到这一题They had just reached the middle when there came a great shout behind them.这一句应该用when 可是从句是过去时 主句
一、when可以和延续性动词连用,也可以和短暂性动词连用；而while和as只能和延续性动词连用.
① Why do you want a new job when youve got such a good one already?（get为短暂性动词）你已经找到如此好的工作,为何还想再找新的?
②Sorry,I was out when you called me．（call为短暂性动词）对不起,你打电话时我刚好外出了.
③Strike while the iron is hot．（is为延续性动词,表示一种持续的状态）趁热打铁.
④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记.
二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while和as从句的谓语动作必须是和主句谓语动作同时发生.
1．从句动作在主句动作前发生,只用 when.
①When he had finished his homework,he took a short rest．（finished先发生）当他完成作业后,他休息了一会儿.
②When I got to the airport,the guests had left．（got to后发生）当我赶到飞机场时,客人们已经离开了.
2．从句动作和主句动作同时发生,且从句动作为延续性动词时,when,while,as都可使用.
①When ／While ／As we were dancing,a stranger came in．（dance为延续性动词）当我们跳舞时,一位陌生人走了进来.
②When ／While ／As she was making a phonecall,I was writing a letter．（make为延续性动词）当她在打电话时,我正在写信.
3．当主句、从句动作同时进行,从句动作的时间概念淡化,而主要表示主句动作发生的背景或条件时,只能用 as.这时,as常表示“随着……”；“一边……,一边……”之意.
① As the time went on,the weather got worse．（as表示“随着……”之意）
② The atmosphere gets thinner and thinner as the height increases．随着高度的增加,大气越来越稀薄.
③As years go by,China is getting stronger and richer．随着时间一年一年过去,中国变得越来越富强了.
④The little girls sang as they went．小姑娘们一边走,一边唱.
⑤The sad mother sat on the roadside,shouting as she was crying．伤心的妈妈坐在路边,边哭边叫.
4．在将来时从句中,常用when,且从句须用一般时代替将来时.
①You shall borrow the book when I have finished reading it．在我读完这本书后,你可以借阅.
②When the manager comes here for a visit next week,Ill talk with him about this．下周,经理来这参观时,我会和他谈谈此事.
三、when用于表示“一……就……”的句型中（指过去的事情）.
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／ Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼,就有人在敲门了.
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．我刚一走进房门,电话就响了.
● when 解析版
〔引导时间状语从句〕具体地说,它有以下几种含义：
1．表明一个动作发生的时候,另一个动作正在进行之中.例如：
When the teacher came into the classroom ,we were reading English．当老师走进教室时,我们正在读英语.
2．表明当某一动作正在进行时,另一动作发生了.如：
When Kate was flying a kite,she found a wallet lying on the ground．凯特正在放风筝时,她发现地上有个钱包.
〔特别提示〕当when从句放在主句之后时,它更强调某一动作的突然性,此时的when相当于and then,and suddenly,just at that time.如；
1．We were watching TV when the telephone rang．（＝We were watching TV and suddenly the telephone rang．）我们正在看电视,（突然）电话铃响了.
试比较：When we were watching TV,the telephone rang．我们正在看电视时,电话铃响了.
2．The boys were playing football when it began to rain．男孩子们正在踢球时,（不料）开始下雨了.
3．I was taking a walk when I came across Lily．我正在散步时,（没想到）遇见了莉莉.
特别是主句中有just,或when从句中有suddenly时,这种突然性更为明显、强烈.例如：
4．He was just falling asleep when he heard someone shout,“Stop the thief!”他刚要入睡,突然听到有人喊：“抓贼!”
5．We were doing our homework at school last night when the lights went out．昨天晚上我们正在学校写作业时,灯（突然）灭了.
〔相关链接〕when引导的状语从句除了上述意义之外,也常具有其他一些含义：