Where’s your pen?—It’s _____my pencil case.[ ]

Although it seemed to be ______ uncomfortable experience, he still found it ______ fun to learn diving.

Could you please tell Lucy that I want to talk to her? —Sure, I will tell her as soon as she _______ back.

Excuse me, is this ______ ipad?— No, it’s not mine. It’s my friend’s.

He argued _______ smoking, and insisted that it was ________ argument that smoking was harmful to health.