Every means , but none proved .
| A．have tried; a success | B．have been tried; successful |
| C．has tried; to be successful | D．has been tried; successful |
It is thought that meteories (陨星)may hold clues about the ________of life on Earth .
| A．origin | B．reserve | C．basis | D．evidence |
He is having a family party in ________of his 84th birthday .
| A．favour | B．celebration | C．harvest | D．feast |
It is important to know about the cultural differences that________cause problems.
| A．must | B．dare |
| C．need | D．may |
When Premier Zhou Enlai was alive，he________work from morning until night every day，dealing with numerous affairs.
| A．would | B．could |
| C．must | D．might |
—May I tell this to my close friend?
—No，you________.Never let anybody else know about it.
| A．needn’t | B．shouldn’t |
| C．mustn’t | D．can’t |