The whole building _____ burned down, but the heavy rain _____.
| A．might have; would help |
B．could have been; helped |
C．must have; helped |
| D．should have been; was helping |
Messages ______ be changed from sound into electricity before they ______ be sent by radio.
| A．must; will | B．have to; can | C．can; must | D．need; may |
He _____ his parents that he has failed in the exam.
| A．dares not tell | B．dares not telling | C．dare not tell | D．dares not to tell |
—The poor people lived near the highway.—_____ very noisy.
| A．It must have been | B．They must be | C．That might be | D．There must be |
As is natural, a man as old as he ______ be very forgetful.
| A．can | B．must | C．should | D．would |