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

A: What is he doing?

B: He is writing ______.

[    ]

　　A. in a paper    B. on any book    C. by pencil    　　D. with a pen