问题补充:
Great changes in the small city in the last 20 years.
A. have taken place
B. took place
C. had taken place
D. are happening
答案:
(答案→)A. have taken place
B. took place
C. had taken place
D. are happening
解析:考查时态:时间是in the last 20 years,和现在完成时连用,句意是:在过去的里,这个小镇已经发生了巨大的改变。选A。