【题目】 The book was written in 1946, _________the education system has witnessed great changes.
A. when B. during which
C. since then D. since when
在线课程【答案】D
【解析】
试题分析：since when中的when指1946，since when指的是since 1946，即指“自1946年起”。注意不要误选C，如果将C改为and since then，则可选C。