Mary _______ her mother with the housework, but she didn’t.
| A．must have helped | B．ought to have helped |
| C．must help | D．should help |
31. The room is in a terrible mess; it _______ cleaned.
| A．can’t have been | B．shouldn’t have been |
| C．mustn’t have been | D．wouldn’t have been |
30. Please write a notice for the students and ______ .
| A．put it up | B．put up it | C．put it on | D．put on it |
29. If city noises____from increasing, people___shout to be heard even at the dinner table 20 years from now.
| A．are not kept; will have to | B．are not kept; have to |
| C．do not kept; will have to | D．do not kept; have to |
28. The farm as well as its neighboring hills we once spent so much time ____ on a new look as recently as last year.
| A．on having taken | B．has taken | C．on has taken | D．having taken |
27. _____ some of the juice — perhaps you'll like it.
| A．Trying | B．Have tried | C．To try | D．Try |