问题描述：
since then &since when
The book was written in 1946,_______ the education system has witnessed great changes.
A.since when
B.since then
为什么选A不选B?
The book was written in 1946,_______ the education system has witnessed great changes.
A.since when
B.since then
为什么选A不选B?
问题解答：
我来补答展开全文阅读