--- Did you find the missing couple in the mountain yesterday?
--- No, but we _______ to get in touch with them ever since.
| A．have tried | B．had tried |
| C．have been trying | D．had been trying |
No matter how much you’ve learned and how high a standard of education you have had, you must _______ the people heart and soul.
| A．serve | B．serve for |
| C．serve to | D．serve on |
. If you want to sell your product you must _____ it.
| A．advertise | B．advertise for |
| C．advertise on | D．advertise to |
New medicines and instruments ______ every day to extend life.
| A．develop | B．are being developed |
| C．are developing | D．have developed |
A red sky in the morning ______ to be a sign of bad weather.
| A．says | B．is saying |
| C．has said | D．is said |
Hundreds of jobs _______ if the factory closes.
| A．lose | B．will be lost |
| C．are lost | D．will lose |