既能用where又能用in which的情況：
引導定語從句，在定語從句中作地點狀語，從句與先行詞的搭配缺少介詞in時，既能用where又能用in which。
（1）This is the house where/in which he used to live.
這是他過去住的房子。
（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.
這所舊學校現在已變成一個大型的現代化工廠，每年生產許多彩色電視機。