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。