新东方考研语法讲堂82

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3、表示与将来事实相反的假设，对将来表示怀疑，或将来的动作不太可能实现时，条件状语从句和主句的谓语动词有以下形式：（见表）
    条件状语从句的动词形式(三种)主句的动词形式
    (1)if十主语+动词过去式(be的过去式用were)，通常要与一个表示将来的时间状语连用.
    (2)If+主语(任何人称和数)+should+动词原形
    (3)if+主语(任何人称和数)+were to+动词原形I(we)should+动词原形
    主语+would (might, could)+动词原形
    请看以下句子：
    1）If it rains tomorrow, our picnic will be put off. (说明：The weather has been very changeable these days.) 条件状语从句的谓语动词用现在时，表示说话人认为下雨的可能性很大。
    2）If it rained tomorrow, our picnic would be put off. (说明：The weather has been very good these days.) 条件状语从句的谓语动词用过去时，表示说话人认为下雨的可能性不大。
    3）If it should rain tomorrow, our picnic would be put off. (万一明天下雨，我们的野餐就推迟)。条件状语从句的谓语动词用should＋动词原形，说明下雨的可能性很小或没有可能，如果下雨，那将是出乎意料的。
    4）If it were to rain tomorrow, our picnic would be put off.这句话与上一句意思几乎一模一样。
   
    If I saw him tomorrow, I would pass your note to him.
    If she were to miss the train tomorrow, she might come back and start off again the day after tomorrow.
   
    万一你失败了，你准备怎么办？
    If you should fail, what would you do?
    要是我明天真的见到她，我就把真相告诉她。
    If I were to see her tomorrow, I would tell her the truth.
    万一明天下雨，会议就推迟。
    If it were to rain tomorrow, the meeting would be put off.
    我打赌巴西会赢得世界杯。要是巴西输了，我就请你搓一顿。
    I bet Brazil will win the World Cup. If it should lose, I would treat you a meal.