问题
选择题
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
D。
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。