(By the time) she got to class,the teacher has already started teaching Awhen Bbefore为什么不能用before?对不起应该是 had already started..

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(By the time) she got to class,the teacher has already started teaching Awhen Bbefore为什么不能用before?对不起应该是 had already started..
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(By the time) she got to class,the teacher has already started teaching Awhen Bbefore为什么不能用before?对不起应该是 had already started..
(By the time) she got to class,the teacher has already started teaching Awhen Bbefore
为什么不能用before?
对不起
应该是 had already started..

(By the time) she got to class,the teacher has already started teaching Awhen Bbefore为什么不能用before?对不起应该是 had already started..
原来用的By the time是指一个时间点,所以应当用when.before 是一个时间段了.

before是在---之前的意思。
先看主句，主句用的是has+done，说明老师已经开始讲课了。
然后看从句，by the time的意思是在----的时候，引导时间状语从句，所以when是最合适的。before与when相比，不适合，主要是主句的时态限制了。应该是 had already started.......

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before是在---之前的意思。
先看主句，主句用的是has+done，说明老师已经开始讲课了。
然后看从句，by the time的意思是在----的时候，引导时间状语从句，所以when是最合适的。before与when相比，不适合，主要是主句的时态限制了。

收起

用when，主句往往用过去进行。e.g. When she got to teh class, the teacher was having the class.
用before，才能体现出过去的过去，用过去完成。

主句用的是had+done，说明老师已经开始讲课了。
从句中，by the time的意思是在----的时候，引导时间状语从句，用when是对的。

那样时态不对

动词填空：She ( ) by the time he got back.(go ) by the time she got to by the time she got up As time( )(go) by,the little girl grew up.As time( )(go) by, by the time she went outside什么意思 有by the time 就用过去完成时吗 比如by the time of last year ,she.是不是要用过去完成时? She had gone by the time he got back 其中的by the time 能用when 或while替换吗 She can go there by by the time ,by then By the time by the time time pass by 与 time go by 有什么区别? 是Time gose by还是Time go by…… as time go by,as time went by哪个对 as time went by 和as time go by go by the by the time she is twenty she___almost every where in the world! 翻译By the time she got to class,the teacher had already started teaching