Only in 1996 the determination and patience of the scientists with a breakthrough at last .
| A．were ; paid off | B．did; pay back | C．did ; pay off | D．did ; pay for |
相关试题
I have no _______ to the plan, so long as it would not cost too much.
| A．refusal | B．comment | C．idea | D．objection |
The radiation amount of a mobile phone for two half-hour periods per day is equal to _______ to an X-ray for ten seconds.
| A．expose | B．exposing | C．exposed | D．being exposed |
—Another cup of coffee? That’s your third since lunch.
—Yeah, well, I ____ all night preparing for my history exam. I can hardly keep my eyes open.
| A．stayed up | B．have stayed up | C．have been staying up | D．will stay up |
. The notice says that only when your identity has been checked _____. 
| A．will you allow in | B．will you be allowed in |
C．you will allow in | D．you will be allowed in |
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