小学英语语法知识点学习：时间介词辨析（下）
1. 表示期限等用 before, by, until/till, (from...) to, within, in
a) before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？
