the book was written in 1946,{since when }the education system has saw great changes.请说明一下括号中为什么用since when而不用since which,when为何能指代1946, 这是什么从句since when有无这种特殊用法在定语从句只19

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the book was written in 1946,{since when }the education system has saw great changes.请说明一下括号中为什么用since when而不用since which,when为何能指代1946,  这是什么从句since when有无这种特殊用法在定语从句只19

the book was written in 1946,{since when }the education system has saw great changes.请说明一下括号中为什么用since when而不用since which,when为何能指代1946, 这是什么从句since when有无这种特殊用法在定语从句只19
the book was written in 1946,{since when }the education system has saw great changes.
请说明一下括号中为什么用since when而不用since which,when为何能指代1946,
这是什么从句
since when有无这种特殊用法在定语从句只1946

the book was written in 1946,{since when }the education system has saw great changes.请说明一下括号中为什么用since when而不用since which,when为何能指代1946, 这是什么从句since when有无这种特殊用法在定语从句只19
其实,这里since when要表明的是一段时间的概念,而since which 只是一个点的时间概念.看看后面的句子,这种改变并不是一蹴而就的.是需要经过一段时间的积累的.所以,when,指代的是1946及以后的一段时间,而并是单单的1946.

时间状语从句。。因为是在那一年education system发生了巨大变化,而不是那本书发生了巨大变化
是这样的,用which,指“the book was written in 1946”这件事了,而句子是为了强调那个时间点

时间状语从句。。因为是在那一年education system发生了巨大变化,而不是那本书发生了巨大变化

因为时间状语从句用when来引导,所以用since when。地点状语从句用where来引导,例如from where。