since then &since whenThe book was written in 1946,_______ the ed_英语解答

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?

人气：268 ℃　时间：2019-12-07 23:40:30

解答

since when 作为定语从句修饰1946.
如果是1946年发生的事,可以直接使用when
但句中给的事情是一直持续到现在的事情,故用since when