—— I can’t get through to the general manager’s office anyhow.
—— The line is busy. Someone _____ the telephone.
| A．must use | B．uses | C．must have been using | D．must be using |
Your phone ______ for several minutes now. Why don’t you answer it?
| A．had rung | B．rang |
| C．has been ringing | D．was ringing |
You can’t see things clearly through a telescope unless it is _____ correctly to your sight.
| A．adjusted | B．examined | C．checked | D．tested |
It is said that many streets in this city have been ______ for cultural protection.
| A．left out | B．carried out | C．marked out | D．stood out |
I tried to ______ Tom last night, but no one answered the phone.
| A．call up | B．call on | C．call off | D．call for |
The ______ of air and water makes it impossible to live on the moon.
| A．presence | B．absence | C．dependence | D．evidence |