全国大众英语测验语法——带to的模样形状动词
带to的模样形状动词有四个：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，否定形式应予以留意：
Do they have to pay their bill before the end of the month?
She didn't use to play tennis before she was fourteen.
You ought not to have told her all about it.
Ought he to see a heart specialist at once.?
ought to自己作为模样形状动词利用。其他的词作为实义动词利用，变疑问，否定时，须有do等助动词帮助。
典范例题
Tom ought not to ___ me your secret, but he meant no harm.
A.have toldB.tellC.be tellingD. having told
谜底A。因为后句为过往时，通知秘密的举措又发作在其前因，此地使用过往完成时，但它在模样形状动词 ought to后，所以用have。