Question

Jane is back in May,by (when) the door should be fininshed.

括号里为什么用when , 此时when是关系代词吗？
还是by后面的一整句都是时间状语，意思是Jane应该在5月份门大概修好的时候回来？

Answer 1

句子翻译： Jane 五月回来， 到时门必须修好。 when是代词 代指jane回来的时候 五月 by (sometime）指在。。。之前 至于什么代词 也不太清楚

Answer 2

Jane五月份回来，到那时门应该修好了。
when 关系副词，指代的是主句的May ,如果把定语从句单用一个句子表达，就是The door should be finished by May.

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为什么不能用by which?

追答

现在想表达“截止。。。时间”所以用by when
如He got home at 8 pm ,by when many people had finished dinner and were wlking in the yard.
看下面例句可以用by which
He bought a used car,by which he could go to and from work conveniently.

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你的意思是which不能代时间？
那这里的when应该是代词呀