单选题
1.The pen_______he is writing is mine.
A.with which
B.in which
C.on which
D.by which
正确答案：A
答案解析：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。