since then &since when

来源：学生作业帮编辑：作业帮分类：英语作业时间：2024/05/19 13:17:05

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?

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

since then &since when since when ,since then的区别（在线等） since when和since since when since then和so Since then it goodbye since/from then ever since then ever since 和 since then 的区别, since then可以说成 since that time But then /Before then / Since then/ Until since