_______ we are doing has never been done before.
| A．That | B．What |
| C．Which | D．Whether |
.
The advertisement says the vacuum cleaner (吸尘器) can ______ everything from the floor. Do you believe it?
| A．pick up | B．take up | C．make up | D．put up |
.
When I knew Mary made every effort ______ the homeless, I could not but ______ her.
| A．to help; admire | B．to help; to admire | C．helping; admire | D．help; admiring |
.
About 71% of the earth’s surface ______ covered with water, but 20% of the world population ______ have access to safe drinking water.
| A．is; doesn’t | B．are; don’t | C．are; doesn’t | D．is; don’t |
.
— Have you thought of a theme for your poster yet?
— No, I ______ a lot about it, but I haven’t decided.
| A．will think | B．have been thinking | C．had thought | D．was thinking |
.
______ left before the deadline, it doesn’t seem likely that John will finish the job.
| A．Though such a short time | B．Because such a short time |
| C．With such a short time | D．As such a short time |