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if条件状语从句谓语动词

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if条件状语从句谓语动词
请帮忙解答一下if条件状语从句的三种谓语动词形式,就是表示对未来、现在、过去的假设,主从句谓语动词都是什么形式.
if条件状语从句谓语动词
1、表示与现在事实相反的情况:
从句:If 主语+过去时(Be动词用were)
主句:主语+should/would/could/might+do
例句“1.If I were you,I would take an umbrella.
如果我是你,我会带把伞.(事实:我不可能是你)
2.If I knew his telephone number,I would tell you.
如果我知道他的电话号码,我就会告诉你.(事实:不知道)
2、表示与过去事实相反的情况
从句:If 主语+had+done
主句:主语+should/would/could/might+have done 
eg:
1. If I had got there earlier,I should/could have met her.如果我早到那儿,我就会见到她.
(事实:去晚了)
2.If he had taken my advice,he would not have made such a mistake.如果他听我的劝告的话,就不会犯这样的错误了.
(事实:没有听我的话)
3、表示对将来情况的主观推测
主句:主语+should/could/would/might+do 
从句:①if+主语+were to do
②if+主语+should/would/could/might+do
③if+主语+did(动词过去式)/were [1]
eg:
1.If he should come here tomorrow,I would talk to him.
如果他明天来这儿的话,我就跟他谈谈.(事实:来的可能性很小)
2.If there were a heavy snow next Sunday,we would not go skating.
如果下周日下大雪,我们就不能去滑冰了.(事实:下雪可能性很小)