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 |
There was a heavy curtain ________ the light.
| A．blocking out | B．preventing from | C．blocking in | D．taking off |
. These old buildings possibly __________ the Ming Dynasty.
| A．dated back to | B．date back to | C．date back | D．are dated back to |
The government announced that six highways by the end of last year.
| A．built | B．had built | C．have been built | D．had been built |
With his eyes _______ on me, he came towards me.
| A．fixed | B．fixing | C．to fix | D．were fixed |
Humans are destroying nature day by day, _____of course, will cause punishment sooner or later.
| A．who | B．which | C．it | D．that |