托福语法辅导：带to的情态动词

会计考友

带to 的情态动词有四个：ought to， have to， used to， be to， 如加上have got to （=must）， be able to，为六个。它们的疑问、否定形式应予以注意：
' t" d% N- h% J% B' L    Do they have to pay their bill before the end of the month？
0 @9 a2 |3 p: B" g9 d) q  S    She didn't use to play tennis before she was fourteen.
' @, K7 {( O" k2 g    You ought not to have told her all about it.
" v% B& E, V9 e. k' d    Ought he to see a heart specialist at once.？
( x* r4 I" j/ M& p- s    ought to 本身作为情态动词使用。其他的词作为实义动词使用，变疑问，否定时，须有do 等助动词协助。
    典型例题
    Tom ought not to ___ me your secret， but he meant no harm.
8 V8 T2 ?4 s+ \, t" _& b) _( L% `9 u    A. have told　B. tell　C. be telling　D. having told
    答案A.由于后句为过去时，告诉秘密的动作又发生在其前因，此地应用过去完成时，但它在情态动词 ought to 后，所以用have told.