by+时间的用法

表示时间，指“最迟在……之前”“到……的时候已经”，此时要注意它所连用的时态。

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He was very tired by the evening.

他到晚上已经很累了。

He has read about 40 pages of the book by now.

现在这本书他已读了大约40页。

We will have finished the work by next month.

到下个月我们就会干完了这工作。

By the time the doctor arrived the patient had died.

在医生到达时，病人已经死了。

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