11.He was busily engaged ______ writing letters.
A. on
B. in
C. with
D. by
12.Do remember to ______ the light when you leave the room.
A. turn up
B. turn on
C. turn off
D. turn down
13.The atmosphere consists of an ocean of gases ______ miles high.
A. hundreds
B. hundreds of
C. of hundreds
D. of hundreds of
14.Not only the students but also the old teacher ______ been changed.
A. was
B. were
C. has
D. have
15.—— ________ I had!
—— You really suffered a lot.
A. What a time
B. What time
C. How a time
D. how time
