while when______ we thank you for your enquiry,we regret bei

when引导的时间状语从句,常见题型里一般这几种时态：1.主句过去进行时,从句一般过去时.2.主句将来时,从句一般现在时（有时候也会用现在完成时）,当然,也会主句是过去将来时（少部分题目还会用was/were about to do表示将来时）,从句是一般过去时.
while引导的时间状语从句,只要保证while后面从句的时态用进行时就可以了,主句用不用进行时无所谓.
当然,while还会引导一种对比的状语从句,这只要时态统一就可以了,比如I like basketball while he likes football.

两者的区别如下：
①when是at or during the time that,既指时间点,也可指一段时间；
while是during the time that,只指一段时间,因此when引导的时间状语从句中的动词可以是终止性动词,也可以是延续性动词,而while从句中的动词必须是延续性动词.
②when 说明从句的动作和主句的动作可以是同时,也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生.
③由when引导的时间状语从句,主句用过去进行时,从句应用一般过去时；如果从句和主句的动作同时发生,两句都用过去进行时的时候,多用while引导,如：
a.When the teacher came in,we were talking.
当此句改变主从句的位置时,则为：
While we were talking,the teacher came in.
b.They were singing while we were dancing.
④when和while 还可作并列连词.when表示“在那时”；while表示“而,却”,表对照关系.如：
a.The children were running to move the bag of rice when they heard the sound of a motor bike.
孩子们正要跑过去搬开那袋米,这时他们听到了摩托车的声音.
b.He is strong while his brother is weak.
他长得很结实,而他弟弟却很瘦弱.
when; while 当……时候
while能用when代替; 但是when却不一定能用while代替.
while+从句,动作一定会延续
when+延续性动词/瞬间动词; when he arrived
when he died
when,while强调动作同时发生
过去进行时 :
在过去的某一点时间,或者是过去某一动作同时发生的另外一个动作
瞬间动词(arrive)无进行时态
I am arriving 进行时态表示将要
When he arrived,I was having dinner.
同时发生的两个动作,均用过去进行时
When I was doing my homework,my mother was cooking.
When my mother was doing the housework,my father was watching TV.
同时发生的两个动作
1.一个用一般过去时,另一个用过去进行时
2.分工的情况,均用过去进行时
When the plane arrived,...were waiting inside the main building
while others were waiting on...
While...
...were keeping guard at the door,two others opened the parcel.
表面上是分工,两个动作同时发生,不是同时开始同时结束,延续时间不一致,
长一点时间的动作用进行时态,短时间的动作用过去时.
When someone knocked at the door,I was having dinner.
when和while引导的时间状语从句与这一时态连用.所以区别when和while的用法成了这一单元的难点.（一）、when,while都有“当……时候”的意思.when既可表示某一点时间,也可以表示某一段时间 .在when引导的时间状语从句中,其谓语动词可以是延续性的,也可以是非延续性的,可与主句中的谓语动词同时发生,也可在其后发生.例如：1、I was just reading a book when she came into my room.她走进我房间时,我正在看书.2、Were you writing when the teacher came in?老师进来的时候,你在写信吗?3、When he was a child he was always trying out new ideas.他小时候就常常试验一些新的设想.（二）、while只能表示某一段时间,不能表示某一点时间.在while引导的时间状语从句中,其谓语动词只能是延续性的,而且也只能与主句中的谓语动词同时发生或存在.例如：1、While Jim was mending his bike,Lin Tao came to see him.正当吉姆修自行车时,林涛来看他.2、You can’t do your homework while you’re watching TV.你不能一边看电视一边做家庭作业.（三）、另外,when和while的区别还在于：while引导的时间状语从句多用进行时态,而when引导的时间状语从句多用一般时态.例如：1、While they were talking ,the bell rang.正在他们谈话的时候,上课铃响了.2、I was doing my homework when my mother came back home yesterday evening.昨天晚上妈妈回家的时候,我正在做家庭作业.
when/while都可做并列连词．前者表and at that time,(这时,突然),后者表对比,可译为”然而”
I was going downstairs when the telephone rang.
Lucy is in blue while Lily is in green.
when后加瞬间动词 while后也可加持续性动词

在都表示“当……的时候”时,while只接持续性动词或者说是动词的ing形式,而when则没有限制,短暂性动词和持续性动词都可以.至于ed,用while也只能接完成进行时.