1)may(might)have+donesth,can(could)have+donesth 表示过去，推测过去时间里可能发生的事情。
Philipmay(might)havebeenhurtseriouslyinthecaraccident.
Philipcan(could)havebeenhurtseriouslyinthecaraccident.2) musthave+donesth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。
---Lindahasgonetowork,butherbicycleisstillhere.
---Shemusthavegonebybus.3)oughttohavedonesth,shouldhavedonesth
本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。
Yououghtto(should)havebeenmorecarefulinthisexperiment.
Heoughtnottohavethrowntheoldclothesaway.（事实上已扔了。）
oughtto在语气上比should要强。4)needn'thavedonesth 本没必要做某事
Idressedverywarmlyforthetr ip,butI needn'thavedoneso.Theweatherwashot.5)wouldliketohavedonesth 本打算做某事
Iwouldliketohavereadthearticle,butIwasverybusythen.
