摘要：4．The book was written in 1946. the education system has witnessed great changes. A．when B．during which C．since then D．since when 解析:句意:这本书写于1946年.从那时起教育体制发生了巨大变化.因为从句中时态为现在完成时.故选since when来引导这一定语从句.A.B两项引导的从句应使用过去某种时态,C项只是充当后面从句中的时间状语.而不能充当引导词来引导该从句.故排除. 答案:D
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The book was written in 1946， the education system has witnessed great changes.
A. when B. during which C. since then D. since when
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