If you are traveling ________ the customs are really foreign to your own, please do as the Romans do．
A.in whichB.whatC.whenD.where在线课程D
解析：
根据句意“如果你在一个风俗不同的地方旅行的话，请入乡随俗。”句中需要一个地点状语，而in which只有在定语从句中的某些情况下才可以与where替换。如：This is the factory where/in which my father used to work。还要注意区分where与wherever, wherever相当于no matter where，引导让步状语从句。