核心问题
I came here in 1950, since when I have been engaged in this work. 请解释 when 及 since when 从句。
词典解答
如同 as 和 which 一样,关系副词 when(不要与从属连词 when 相混淆)以及某些介词 + when 也能引导修饰句子的非限制性定语从句(sentential relative clauses),即不是修饰名词中心词的定语从句。这时 when 所代表的常常是前面的句子所提供的时间背景。
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Two years ago I bought a packet of your razor blades, since when I have used no others. (CGEL) 两年前我买了一包你们的剃须刀片，从那以后我再没用过别的。
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They settled in Seattle, by when she had obtained a master's degree in economics. (CGEL) 他们在西雅图住了下来，在那之前她已经获得了经济学硕士学位。
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She joined the editorial staff of a local newspaper, since when she has contributed to various monthlies. (CGEL) 她加入了一家地方报纸的编辑组，从那时开始她为各式各样的月刊投稿。