25. A team of scientists _____ the effects of acid rain over the last twenty-year period.
A
studied
B
had studied
C
is studying
D
has been studying
25. ––Have you asked Peter for advice?
––No, he ______ someone, so I didn’t disturb him.
31.Social and cultural activities for senior citizens ______ over the past several years.
34.Wait a moment. The director _____ her assistant pick up some sandwiches for the meeting.
句意:一组科学家在过去20年里一直在研究酸雨的影响。根据时间状语over the last twenty-year period可知选D。
现在完成时及其被动式
判断结构
抓不住要点
容易