21. The doctor put me on      diet and advised me to go out for      walk after supper.
    A. an; /                      B. a; a                             C. /; a                             D. /; / 
22. — I’m sorry, I’m late.
  —     . The meeting hasn’t started.
    A. I’m afraid not.                                             B. It doesn’t matter.
    C. You’re welcome.                                           C. Don’t mention it.