Scientists believe that it might be several years ______ the medicine can be used on human beings.
| A．since | B．when | C．before | D．until |
相关试题
Danny left word with my secretar
y he would call again in the afternoon.
| A．that | B．who | C．as | D．which |
The look on his face showed that he was greatly of being left alone in the house.
| A．terrified;terrifying | B．terrified;terrified |
| C．terrifying; terrifying | D．terrifying; terrified |
Having a large family to support, Mr.Johnson had to work in the evening.
| A．four another hours. | B．more four hours. |
| C．other four hours. | D．four extra hours. |
—When did you get to know the professor over there?
—It was at the work shop we did reserch to gether two years ago.
| A．that | B．there | C．which | D．where |
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