The new China was founded in 1949 great changes have taken place.A. since whenB. after w

问题补充：

The new China was founded in 1949, great changes have taken place.

A. since when

B. after which

C. in which

D. when

答案：

(答案→)A. since when

B. after which

C. in which

D. when

解析：考查定语从句。句意：新中国在1949 年建立，从那时候起中国就发生了重大变化。现行词为1949,，从句中缺少时间状语从句。所以选A。