The pen _______ he is writing is

The pen _______ he is writing is mine.
A、with which
B、in which
C、on which
D、by which
【正确答案】：A
【题目解析】：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。