before和by（不迟于…,在…之前）如何区别?是不是后面加的时间不同?

efore与by
before 指“在……之前” ：
Please come before ten o'clock.请10点以前来.
by 指“在……前（时间）；截至（到）……”：
How many English books had you read by the end of last year?到去年年底以前你看过多少本英文书?
表示“在……以前”时,before 与 by 基本可通用.但 by 还有“截至……为止”之意：
How many models have you made by the end of last month?截至上月底你做了多少个模型?