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by which之所以比in which更能“强调这个process的效果”，是因为by在古英语时期接名词的工具格，它比介词in一定程度上更能强调工具产生的施动效果，又如They took it over by force.中的“by force”。
用in which也完全正确，只是少了点强调的意蕴。
【 在 restlessmind 的大作中提到: 】
: 也是，有人解释了by which和in which的区别。 by which是强调这个process的效果，而in which是在这个process中发生了什么。
: "A process by which" describes the effect of the process. "A process in which" describes what happens in the process.
: For example:
: ...................
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