I’m going back to my home town this winter, ( ) I won’t have enough time to buy presents.

　　A. by which

　　B. in which

　　C. at which

　　D. on which

　　【答案】B。逗号加which 是非限定性定语从句的标志，而根据题干的意思，知道后半句是指：他这个冬天将要回他家乡，(但是)到那个时候，他没有足够的时间买礼物。所以修饰的先行词是this winter，能与之搭配的，是介词in，选B。