The pen he is writing is mine. A. with which B. in which C. on which D. by which

The pen he is writing is mine.
A. with which
B. in which
C. on which
D. by which

(答案→)A. with which B. in which C. on which D. by which解析：. with which是介词+关系代词结构,常用来引导定语从句.with有用的意思,介词之后只能用which,不能用that. with which在定语从句中作状语,即he is writing with a pen.

感谢回答，我学习了