2012考研必备：考研英语语法精要(47)

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3.时间状语从句的常考知识点
    (1)before表示汉语的 “只有/必须……才能”。如:
    Electronics must be programmed before they can work.必须为计算机编好程序它才能工作。
    New ideas sometimes have to wait for years before they are fully accepted.有时候新的思想必须等待多年以后才能被人们完全接受。
    (2)when引导时间从句时，如果出现在后半句，则表示“这/那时突然”。如：
    He was almost hurt when the bus came to a sudden stop.(1991年6月四级考题)
    I have just started back for the house to change my clothes when I heard the voices.
    (3)when it comes to 是习惯用法，意为“当谈到……时”。如：
    Doing your homework is a sure way to improve your test scores, and this is especially true when it comes to classroom tests.
    (4)名词短语、介词短语each /every time, the moment/second/minute, in the time, by the time起连词作用。如:
    I hope her health will have improved greatly by the time we come back next year.
    If individuals are awakened each time they begin a dream phase of sleep, they are likely to become irritable even though their total amount of sleep has been sufficient.
    My pain must have been apparent the moment I walked into the room, for the first man I met asked sympathetically: “Are you feeling all right?”
    Mercury’s velocity is so much greater than the Earth’s that it completes more than four revolutions around the Sun in the time it takes the Earth to complete one.
    (5)副词directly, immediately, instantly, now引导时间从句, 相当于as soon as。如:
    The policemen went into action directly they heard the alarm.