The doctor said jokingly that his own infection of the virus _______ the discovery of a vaccine (疫苗)of the disease.
| A．stood for | B．called for | C．paid for | D．contributed to |
Most people think that it is _____ to spend some time surfing the Internet, but we shouldn’t be too dependent on it.
| A．worth | B．worthwhile | C．worth of | D．worthy of |
--- Have you handed in your schoolwork yet?
---Yes, I have.I guess it _____ now.
| A．has graded | B．is graded |
| C．is being graded | D．is grading |
We _____ have bought so much food now that Suzie won’t be with us for dinner.
| A．needn’t | B．mustn’t | C．can’t | D．should |
By the time you wake up tomorrow morning, we _____ in the USA.
A.arriveB.arrived
C.are arriving D.will have arrived
One minute she burst into _____ and the next burst out _____.We just couldn’t catch her mood at any moment.
| A．crying; laughter | B．tears; laughter |
| C．crying; laughing | D．tears; laughing |