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
答案：D
since when引导定语从句。因为句中的谓语has witnessed是现在完成时,所以要用since when。when指代上文中的in 1946,表示“这本书是1946年写的,从那以后,教育体制发生了巨大变化”。