There have been fewer accidents on this highway the speed limit was introduced.

There have been fewer accidents on this highway ________ the speed limit was introduced.

A．before 

B．while

C．after 

D．since

试题答案

D解析：此题考查时间状语从句。句意是：自从设定了速度限制以来，这条高速公路上的交通事故比以前要少了。根据主句中的现在完成时和时间状语从句的一般过去时可以推断出此处要用since 引导这个时间状语从句。