问题补充:
The book was written in 1946, the education system has witnessed great changes.
A. when
B. during which
C. since then
D. since when
答案:
A. when
B. during which
C. since then
(答案→)D. since when
解析:考查定语从句。since when以为“从那时起”,when时间副词,这里指代时间 1946,相当于since when的意思就是since the year 1946。句意:自从1946年起,教育体系经历了巨大变革。