if的用法，请解释
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发布时间：2022-04-22 08:51
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热心网友
时间：2023-10-06 06:00
if的用法如下：
1、表示条件：如果。主句用将来时，if从句用现在时表示将来。
He will come if you invite him.
2、是否：whether连接宾语从句。
I wonder if he is ill.
3、表示虚拟：假如，要是。时态：可以表示过去，现在和将来的情况，它的基本特点是时态退后。
A、同现在事实相反的假设。
一般过去时should(would)+动词原形：If they were here,they would help you.
B、表示于过去事实相反的假设。
过去完成时should(would)have+过去分词：If she had worked harder,she would have succeeded.
C、表示对将来的假想。
一般过去时should+动词原形：If you succeeded,everything should be all right.
were+不定式would+动词原形：If you should succeed,everything would be all right.
should+动词原形：If you were to succeed,everything should be all right.
