When _________ files, I use both sides of the paper.
A. to print
B. prints
C. printing
D. printed
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Turn _______the lights when you leave the room.
A. on
B. off
C. up
D. down
______________ beautiful pen holder!
A. What a
B. What
C. How
D. How a
Air pollution is a ___________ problem all over the world.
A. grows
B. growing
C. grew
D. grown
We should try ____________ white pollution.
A. to reduce
B. reducing
C. reduces
D. reduced