Rock-climbing is a breathtaking activity, very popular nationwide among young people, ______ cooperation as well as courage plays an important role.
| A．who | B．which | C．where | D．of which |
Now there is a danger _________ the ground may fall under the heavy traffic.
| A．whether | B．if |
| C．/ | D．that |
We think it possible _________ the local government will be able to solve the housing problem.
| A．for | B．that |
| C．when | D．How |
She took it for granted _________ I'd be back home an hour later.
| A．that | B．whether |
| C．if | D．When |
_________ caused the accident is still a complete mystery.
| A．What | B．That |
| C．How | D．Where |
It is widely _________ that smoking can cause cancer.
| A．believed | B．think |
| C．say | D．Hoped |