定语从句的两问题,

题目

定语从句的两问题,
1.定语从句The book was written in1946,___the education system has witnessed great changes.
A.when B.during when C.since then D.since when
这是一高考题,据说是相当与since which time
然而我又遇到这样一道题,如
In the office I never seem to have time until after 5:30 p.m.,____ many people have got home.
A.whose time B.that C.on which D.by which
如果就选答案的话,只有选D,答案也是D.但是这就与上题不就冲突了吗,应该是by which time或是by when?

答案

第一句分析正确.
第二句by which就是by which time,因为主句有一个time,为避免重复就不说time了.
when一般用作疑问副词；但有时也可用作疑问代词,作since, until, up to 等少量几个介词的宾语,如until when, since when, up to when.
按道理来讲,第二题的by which time就是等于by when.但语言不仅要讲道理,更要讲习惯.再合乎逻辑的说法,如果大家口头上都不这样说,那也只能认为它是错的.by when这种说法目前我还没见过.