語法練習(xí)

　　Complete the following sentences by circling the missing words.

　　1. Science still a cure for cancer.

　　a. doesn’t find c. hasn’t found

　　b. haven’t found d. aren’t finding

　　2. While he a route to the Indies, Columbus discovered America.

　　a. searched c. had searched for

　　b. was discovering d. was searching for

　　3. Existing reserves of fossil fuel by 2045.

　　a. have been run out c. is going to be run out

　　b. will have run out d. have run out

　　4. If logging of tropical rainforests continues at the present rate, a 30 per cent increase in atmospheric CO2 by the year 2000.

　　a. there will be c. there would be

　　b. there might have been d. there could not have been

　　5. Only by investing heavily in value-added exports from the present trade imbalance.

　　a. the country can emerge c. can the country emerge

　　b. the country might emerge d. the country emerged

　　6. The mystery of the double helix , the scope for genetic engineering dramatically increased.

　　a. having solved c. solving

　　b. having been solved d. solved

　　7. Since the mid-’60s considerable research in embryo transplants .

　　a. has carried out c. has been carried out

　　b. was done d. was carried out

　　8. several hypotheses have been advanced for the disappearance of the dinosaur, no conclusive evidence supports any of them.

　　a. despite c. although

　　b. in spite of d. in spite of the fact

　　9. Until the 16th century the earth to be flat.

　　a. is believed c. believed

　　b. has been believed d. was believed

　　10. If the temperature of the reactor 500C higher meltdown would have occurred.

　　a. was c. was being

　　b. had been d. had