Li Ning was able to set up a school for gymnasts in 1991, he has continued to help young people to achieve their sporting ambitions.
A. when
B. dring which
C. since then
D. since when
网友回答
A. when
B. dring which
C. since then
(答案→)D. since when
解析：考查非限制性定语从句。句意：1991年，李宁为体操运动员修建了一个学校，从那以后，他一直继续帮助年轻人实现他们的体育梦。句中有逗号，是非限制性定语从句，during which=when，since then不能引导定语从句，排除A、B、C。since when从那以后，符合题意。故选D。