问题补充:
In addition to the farming they since the 1990s, the Smiths have started a small business.
A. have done
B. had been done
C. were doing
D. have been doing
答案:
A. have done
B. had been done
C. were doing
(答案→)D. have been doing
解析:考查时态。从时间状语since the 1990s,可知应该使用现在完成时或现在完成进行时,然后根据后面主句的谓语动词have started可推断,do 这个动词还在继续,故使用现在完成进行时。句意:自从20世纪90年以来,史密斯夫妇开了一家小公司,此外他们还一直在做农活。