题目内容:
In the past 50 years, there _____ a great increase in the amount of research _____ on the human brain.
A.was...did
B.has been...to be done
C.was...doing
D.has been...done
参考答案:
答案解析:
In the past 50 years, there _____ a great increase in the amount of research _____ on the human brain.
A.was...did
B.has been...to be done
C.was...doing
D.has been...done