in which引导定语从句，根据句义，可以等于when表示当...时候也可以等于where表示地点I'll never forget these days in which I stayed with you.= I'll never forget these days when I stayed with you.我永远不会忘记我和你待在一起的日子。
This is the city in which I stayed last year.This is the city where I stayed last year.这就是那个去年我待的地方。例句：The English play in which my students actedat the New Year’s party was a great success.“在英语剧中”应用介词in，因此在修饰先行词play的限定性定语从句中也应用介词in与指代先行词play的关系代词which连用，本句中which充当置于定语从句中最前面的介词in的宾语(in which在整个定语从句中充当状语)
