问题
选择题
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
答案：D
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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：D