since then &since whenThe 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?

分类: 作业答案 • 2021-12-19 10:31:47

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?

答

如果选B,
那么一般都是在句首,而且有逗号,"从那时起"
而这里选A,翻译成从(since)后面是从句when引出时间.
如果不用when引出,since+时间点前面就要用完成时态,就是另外一种意思了

答

因为这是从句啊.如果since前是句号就是since then

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