Genetic engineering is helping researchers unravel the mysteries of previously incurable diseases so that they can get its root causes and find cures.

B. was carrying

C. was carried

D. has been carried

 A. advise/ give    

 B. to advise/ to give

 C. advising/ giving   

 D. advising/ to give

A. how long you have studied English

B. how long had you studied English

C. how long you had study English

D. how long you had studied English

A. plainly

B. properly

C. flashily

D. soberly

A. attractive

B. effortless

C. inelegant

D. sophisticated

A. John doesn’t write home once a week any longer.

B. John enjoyed being written home every week when he was abroad.

C. John never forgot to write a weekly letter home when he was abroad.

D. When he was abroad he remembered to write home every week.

A. came out

B. went out

C. pulled out

D. broke out