问题补充:
The book was written in 1946, the education system has witnessed great charges.
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: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,如果将改为and since then,则可选C。