in which引导定语从句，在从句中不作地点状语，而是作方式状语时，用in which；引导定语从句，介词in与从句中某些词语构成固定搭配，用in which。
既能用where又能用in which的情况引导定语从句，在定语从句中作地点状语，从句与先行词的搭配缺少介词in时，既能用where又能用in which。
（1）This is the house where/in which he used to live.
这是他过去住的房子。
（2）The old school has now turned into a large modern factory where/in which a lot of coulour TV sets are produced every year.
这所旧学校现在已变成一个大型的现代化工厂，每年生产许多彩色电视机。
只用in which不用where的情况1.引导定语从句，但在定语从句中不作地点状语，而是作方式状语时，只用in which，不用where。
（1）This is the best way in which we can do the work well.
这是我们把工作做好的最好办法。
2.引导定语从句，介词in与定语从句中某些词语构成固定搭配时，只用in which不用where。
（1）He left his work in which he had been very successful.
他离开了他非常成功的工作。
