___________________ to sunlight for too much time will do harm to one’s skin.
| A．Exposed | B．Having exposed | C．Being exposed | D．To expose |
You cannot tell________looking at someone whether or not he has HIV.
| A．without | B．by |
| C．for | D．with |
The days are gone________you can breathe fresh，unpolluted air or drink clean, unpolluted water in the countryside.
| A．when | B．that |
| C．where | D．which |
Learn some relaxation exercises and do them every time you feel________.
| A．embarrassed | B．stressed |
| C．ashamed | D．impressed |
Many young people don't work hard, and regret it later when the opportunity is gone.They only realize it________it is too late.
| A．when | B．before |
| C．in case | D．until |
Everybody needs calcium, but it is quite possible for a similar person to be totally healthy by eating only________.
| A．as half much | B．as much half |
| C．half as much as | D．half as much |