Scientists say it may be five or six years _______ it is possible to test this medicine on human patients.
| A．since | B．after | C．before | D．when |
_____ in the queue for half an hour,Tom suddenly realized that he had left his wallet at home．
| A．To wait | B．Have waited |
| C．Having waited | D．To have waited |
The library needs _____,but it’ll have to wait until Friday．
| A．cleaning | B．to clean |
| C．being cleaned | D．to being cleaned |
--- Catherine, I have cleaned the room for you．
---Thanks．You _______ it．I could manage it myself．
| A．needn’t do | B．shouldn’t have done |
| C．mustn’t do | D．needn’t have done |
It didn’t take the children long to________ the correct answer．
| A．carry out | B．figure out |
| C．turn out | D．give out |
_____ herself to science, the great scientist took little notice _____ the honors given to her．
| A．Devoted, of | B．Devoting, of |
| C．Devoted, about | D．Devoting, about |