20. The flu is believed________by viruses.
| A．causing | B．being caused | C．to be caused | D．to cause |
As the twentieth century came to a close, the raw materials for a great national literature were at hand, waiting __________.
| A．to use | B．to be used |
| C．to have used | D．to be using |
If you think that treating a woman well means always __________ her permission for things, think again.
| A．gets | B．got |
| C．to get | D．getting |
The wild flowers looked like a soft orange blanket __________ the desert.
| A．covering | B．covered |
| C．cover | D．to cover |
AIDS is said __________ the biggest health challenge to both men and women in that area over the past few years.
| A．that it is | B．to be |
| C．that it has been | D．to have been |
— I was wondering if we could go skiing on the weekend.
— __________ good.
| A．Sound | B．Sounded |
| C．Sounding | D．Sounds |