Ifyouhadaskedhimyesterday,youwouldknowwhattodonow.
       （从句与过去事实相反，主句与现在事实相反。）
        Ifithadrainedlastnight(过去),itwouldbeverycoldtoday(现在).
      
      
      
      16.4虚拟条件句的倒装 
        虚拟条件句的从句部分如果含有were,should,或had,可将if省略，再把were,should或had移到从句句首，实行倒装。
       Weretheyherenow,theycouldhelpus.
       =Iftheywereherenow,theycouldhelpus.
       Hadyoucomeearlier,youwouldhavemethim
       =Ifyouhadcomeearlier,youwouldhavemethim. 
       Shoulditrain,thecropswouldbesaved.
       =Wereittorain,thecropswouldbesaved.
      
      注意：
       在虚拟语气的从句中，动词'be'的过去时态一律用"were"，不用was，即在从句中be用were代替。
       IfIwereyou,Iwouldgotolookforhim.
        如果我是你，就会去找他。
       Ifhewerehere,everythingwouldbeallright.
        如果他在这儿，一切都会好的。
      
      典型例题
       _____todothework,Ishoulddoitsomeotherday.
      A.IfwereI  B.Iwere C.WereI D.WasI
       答案C.在虚拟条件状语中如果有were,should,had这三个词，通常将if省略，主语提前,变成were,should,had+主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说WereInottodo.,而不能说Weren'tItodo.
      
      
      
      16.5特殊的虚拟语气词：should 
      1）Itisdemanded/necessary/apity+that…结构中的主语从句的谓语动词要用should加动词原形，should可省略。
      
      句型：
      (1)suggested
      Itis (2)important    that…+(should)do
      (3)apity
      
      (1)suggested,ordered,proposed,required, demanded,requested,insisted；+(should)do
      (2)important,necessary,natural,strange
      apity, ashame, nowonder
      (3)Itissuggestedthatwe(should)holdameetingnextweek.
      
      
       Itisnecessarythathe(should)cometoourmeetingtomorrow.
      
      2）在宾语从句中的应用
        在表示命令、建议、要求等一类动词后面的从句中。
      order,suggest,propose,require,demand,request,insist,command,insist+(should)do
       Isuggestthatwe(should)holdameetingnextweek.
       Heinsistedthathe(should)besentthere.
      
      
       注意：如suggest,insist不表示"建议"或"坚持要某人做某事时"，即它们用于其本意"暗示、表明"、"坚持认为"时，宾语从句用陈述语气。
       Theguardatgateinsistedthateverybodyobeytherules. 
      
       判断改错:
       （错） Youpalefacesuggeststhatyou(should)beill.
       (对) Yourpalefacesuggeststhatyouareill.
       (错) Iinsistedthatyou(should)bewrong.
       (对) Iinsistedthatyouwerewrong.
      
      3）在表语从句，同位语从句中的应用
        在suggestion,proposal,idea,plan,order,advice等名词后面的表语从句、同位语从句中要用虚拟语气，即（should）+动词原形。
        Myideaisthatwe(should)getmorepeopletoattendtheconference.
        Imakeaproposalthatwe(should)holdameetingnextweek.
      
      
      
      16.6wish的用法 
      1）用于wish后面的从句，表示与事实相反的情况，或表示将来不太可能实现的愿望。其宾语从句的动词形式为：
      
               真实状况 wish后     
      从句动作先于主句动词动作  现在时  过去时
      （be的过去式为were）                
      从句动作与主句动作同时发生 过去时  过去完成时
      （had+过去分词）                  
      将来不大可能实现的愿望   将来时 would/could+
                     动词原形    
      
       IwishIwereastallasyou. 我希望和你一样高。
       Hewishedhehadn'tsaidthat.他希望他没讲那样的话。
       Iwishitwouldraintomorrow.我希望明天下雨就好了。
      
      2）Wishtodo表达法。
       Wishsb/sthtodo
       Iwishtoseethemanager.=Iwanttoseethemanager.
       Iwishthemanagertobeinformedatonce.(=Iwantthemanagertobeinformedatonce.)
      
      
      
      16.7比较ifonly与onlyif 
        onlyif表示"只有"；ifonly则表示"如果……就好了"。Ifonly也可用于陈述语气。
        Iwakeuponlyifthealarmclockrings.只有闹钟响了，我才会醒。
        Ifonlythealarmclockhadrung.   当时闹钟响了，就好了。
        Ifonlyhecomesearly.       但愿他早点回来。
      
      
      
      16.8Itis(high)timethat 
       Itis(high)timethat后面的从句谓语动词要用过去式或用should加动词原形，但should不可省略。
       Itistimethatthechildrenwenttobed.
       Itishightimethatthechildrenshouldgotobed.
      
      
      
      16.9need"不必做"和"本不该做" 
       didn'tneedtodo表示：过去不必做某事,事实上也没做。.
       needn'thavedone表示：过去不必做某事,但事实上做了。
       JohnwenttothestationwiththecartomeetMary,soshedidn'tneedtowalkbackhome.约翰开车去车站接玛丽，所以她不必步行回家了。
       JohnwenttothestationwiththecartomeetMary,sosheneedn'thavewalkedbackhome.约翰开车去车站接玛丽，所以她本不必步行回家了。(Mary步行回家，没有遇上John的车。)
      
      典型例题
       Therewasplentyoftime.She___.
      A.mustn'thavehurried B.couldn'thavehurried  C.mustnothurry D.needn'thavehurried
       答案D。needn'thavedone.意为"本不必"，即已经做了某事，而时实际上不必要。
       Mustn'thavedone用法不正确，对过去发生的事情进行否定性推断应为couldn'thavedone,"不可能已经"。