John took his friends there by a shortcut, ____reduced the drive

John took his friends there by a shortcut, ____reduced the drive from 50 minutes to15.
A、where
B、which
C、that
D、what
【正确答案】：B
【题目解析】：考察非限制性定语从句；先行词是前面的整句话，而不是a shortcut,因为如果是shortcut的话引导词应该紧跟着它，没有逗号。这里之所以有逗号，就是把前面整句话作为先行词，后面的引导词用which，引出后面造成的结果。