【题目】Since the new speed limits ______，the number of accidents in the area has fallen strikingly．
A. were introduced
B. introduced
C. have been introduced
D. have introduced
在线课程【答案】A
【解析】自从新的速度限制被提出，这个区交通事故的数量下降了很多。Since +过去式，主句+现在完成时，为常用句型。故排除C、D． 而since 引导句子中缺少谓语，而speed limits与introduce之间为被动关系故选A