过去完成时should(would)have+过去分词
Ifshehadworkedharder,shewouldhavesucceeded.
Thericewouldnothavebeenburntifyouhadbeenmorecareful.
IfmylawyerhadbeenherelastSaturday,hewouldhavepreventedmefromgoing.
Ifhehadcomeyesterday,Ishould/wouldhavetoldhimaboutit.
含义:Hedidnotcomeyesterday,soIdidnottellhimaboutit.
Ifhehadnotbeenillandmissedmanyclasses,hewouldhavemadegreaterprogress.
含义:Hewasillandmissedmanylessons,sohedidnotmakegreaterprogress.