Although the causes of cancer_____, we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering | C．are uncovering | D．have uncovered |
We had planned to arrive at the park at 9 a.m., but unluckily, the car __ on the way.
| A．broke away | B．broke down | C．broke up | D．broke into |
Even when I am able to get in touch with the manager and tell him your request, I cannot __ he will reply.
| A．stress | B．appeal | C．inform | D．guarantee |
__ will be good for you to spend one hour exercising outdoors every day.
| A．That | B．This | C．It | D．One |
If you are inposition of __ teacher, will you allow your students to play computer games all day long?
| A．/; a | B．a; / | C．the; / | D．the; a |
Once __________sport has become less popular, it has to make __________way for new sport which are more popular to enter into the Olympics.
| A．the；a | B．a；／ | C．／；the | D．the；／ |