if i were you， i would be happy to do it.
　　if we had got the news， we could have prepared earlier.
　　if the job were to succeed， you should work harder.
　　第二大类：从句中用过去时或过去完成时的虚拟语气
　　1) would rather + 从句
　　2) wish + 从句
　　3) if only + 从句
　　4) as if/ as though + 从句
　　5) it’s time + 从句
　　i would rather you didn’t tell me the story now.
　　i would rather you had told me the story yesterday.
　　第三大类：从句中用should加动词原形的虚拟语气，其中should可省略。
　　1) suggest， propose， advise， move(动议)， ask， order， require， request， desire， insist， prefer 等动词后接的宾语从句;
　　2) suggestion， proposal， advice， motion， order， requirement， request， desire， preference等名词后的同位语从句;
　　3) important， necessary， essential， imperative， desirable， advisable， preferable 等形容词用在it is … that…句型中;
　　4) lest， in case， for fear that 等引导的从句中。
　　it is suggested that the meeting (should) be put off.
　　it is my suggestion that the meeting (should) be put off.
　　it is necessary that the meeting (should) be put off.
　　he came to the office earlier lest he (should) miss the important meeting.
　　4.定语从句和名词性从句
　　4.1 定语从句：限制性和非限制性定语从句
　　引导定语从句
　　1)关系代词(在定语从句中作主语、宾语、表语)：which， that， who， whom， whose
　　2)关系副词(在定语从句中作状语)：when， where， why， how
　　名词性从句：主语从句、宾语从句、表语从句、同位语从句
　　引导名词性从句：
　　1)主从连词(不在从句中作任何成分)：that， whether， if
　　2)连接代词(在从句中作主语、宾语、表语)：what， which， who， whom， whose， whatever， whoever…
　　3)连接副词(在从句中作状语)：when， where， why， how
　　4.2 定语从句和同位语从句的区别
　　定语从句对名词进行修饰限制，而同位语从句阐述的是名词的具体内容。从语法上看，that， which在定语从句中做主语或宾语，而同位语的引导词that不在从句中担任任何成分。
　　1) the story (that) he told me may not be true. 定语从句
　　2) the story that he has made a fortune may not be true. 同位语从句
　　4.3 什么时候用介词+which 的形式?
　　如果定语从句缺主语或宾语，用that/ which 形式。如果定语从句缺状语，用介词+which形式。
　　1) the place which i visited last week is very beautiful.
　　2) the place in which i used to live is very beautiful.
　　4.4 which 和 as 引导非限制性定语从句
　　which 和 as 都能引导非限制性定语从句，修饰整个一句话。as有“正如”的意思，而which没有有