Why _______ you be so stubborn? You should think over my advice on this matter.
| A．may | B．shall | C．dare | D．must |
With a good __________ of Chinese, Helen was hired to do the task of communication with the Chinese company.
| A．program |
| B．command |
| C．guidance |
| D．ability |
The teacher commanded that the students __________ the classroom before he returned.
| A．didn't leave |
| B．wouldn't leave |
| C．needn't leave |
| D．shouldn't leave |
Before the tourists set off, they spent much time setting a limit __________ the expenses of the trip.
| A．in |
| B．for |
| C．to |
| D．about |
There is a limit __________ people's life, but no limit __________ the knowledge.
| A．on; to learn |
| B．to; to learn |
| C．on; learning |
| D．to; to learning |
Unfortunately, the research was limited __________ increasing economic profits，__________ protecting the environment.
| A．to; other than |
| B．by; rather than |
| C．to; rather than |
| D．by; more than |