11. — Can I have a day off tomorrow, Mr. Johnson?
   — ________. I can manage without you.
A. Forget it.    B. I’m afraid not.    C. It depends.    D. Of course.
12. ________ with care, one tin will last for six weeks.
A. Use    B. Using    C. Used    D. To use
13. ________ at the door before you enter my room, please.
A. Knock    B. Knocking    C. Knocked    D. To knock