According to the report，the number of animals used in experiments ________ by 30% over the years.
A．was reduced B．has been reduced
C．were reduced D．have been reduced
According to the report，the number of animals used in experiments ________ by 30% over the years.
A．was reduced B．has been reduced
C．were reduced D．have been reduced
B [时间状语over the years常与现在完成时连用；“the number of＋ 复数名词”作主语，谓语动词用单数，且reduce与the number of animals之间是动宾关系，故选B。]