现在：
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）
3 If I were you,I'd like to go home
如果我是你,我会选择回家
4 If there was't the U.S.A,I would choose Australia.
如果没有美国的话,我就会选择澳大利亚.
过去：
1 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）
将来：
1.If he should come here tomorrow,I should/would talk to him.如果他哪天来这儿的话,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：不知能否下雪）
