大家在举例的时候常常会这么说“如果………”，”假设………。.”，即if………
先不说这种举例的好还是坏，就本身的句子而言，很多都是有问题的。
总结了一些if的用法，大家考前看看
先看两个例子：
［Scenery］Sue has lost her watch. She think it may be at Ann”s house.
SUE： I think I left my watch at your house. Have you seen it？
（1） ANN： no， but I”ll have a look when I get home. If I find it， I”ll tell you.
If I find…。， I”ll……
（2） Ann says： If I found a wallet in the street， I”d take it to the police.
If I found……， I”d（=I would）……。.（而不是if I find， I”ll…。.）
这里两个句子有着不同的意思，前者表示Ann觉得她有找到手表的真实可能性。因此才说if I find…。.， I”ll…。.
而后者是完全不同的情况。在这里Ann没有考虑真实的可能性;她在虚拟这一个情景，并不认为真的可以在街上拣到手表。于是才说：if I found……，I”d……
if I do………。和if I did………的区别
用if+过去式（if I found / if you were / if we didn”t等） 表示虚拟的事情，而不是指过去时间发生的事情：
What would you do if you won a million pounds？
I don”t really want to go to their party， but I probably will go. They”d be offended if I didn”t go
Sarah has decided not to apply for the job. She isn”t really qualified for it， so she probably wouldn”t get it if she applied.
If从句中一般不用would：
I”d be very frightened if somebody pointed a gun at me.（而非if somebody would point）
If I didn”t go to their party， they”d be offended（而非if I wouldn”t go）
If …….would可以表示用来请求某人做某事：
I would be grateful if you would send me your brochure as soon as possible.
“Shall I close the door？” “yes， please， If you would.”
Would（“d） / wouldn”t用于句子的主句（不是if从句）
If you took more exercise， you”d （=you would） probably feel healthier.
Would you mind if I used your phone？
I”m not tired enough to go to bed yet. I wouldn”t sleep.
另外，if引导的条件句也能引起倒装，如果要是在作文里用到，也是一个加分点：
先看正常语序。
It would be a serious setback， if the talks were to fail.
If you should need more information， please telephone our main office.
If Alex had asked， I would have been able to help.
倒装是要省略if
it would be a serious setback， were the talks to fail.
Should you need more information， please telephone our main office.
Had Alex asked， I would have been able to help
倒装句比if-从句更加正式。
但是在否定句里面，不可以用缩写
e.g.
Had he not resigned， we should have been forced to sack him（不用hadn”t he…。.）
再多说一下，在写作文的时候，希望大家举例的时候能够写实例，因为实例有它的特指性和唯一行，当然，如果实在你没有经历过，在举例虚拟一个场景的时候， if起头，就不要弄错了。
最后几天， 练练作文， good luck， I give my best bless to all you guys！