________ it is true that a student's most important goal is to do well in his or her studies，it doesn't need to be the only goal.
| A．When | B．As | C．While | D．Before |
The living room is clean and tidy, ________ a dining table already laid for a meal to be cooked.
| A．as | B．which | C．with | D．That |
Scientists say it will be five or six years ________ it is possible to test this medicine on humans．
| A．after | B．before | C．since | D．When |
You are students in the No.168 Senior High School now, but you _______ in different junior high schools for three years．
| A．studies | B．have studied |
| C．studied | D．were studying |
Being injured in the leg made _______ impossible for him to walk his way home．
| A．that | B．which | C．it | D．One |
It is believed that a new kind of drug _____ by the scientists and they are hopeful that they will succeed in a few months．
| A．has been developed | B．is being developed |
| C．is developing | D．has developed |