When something is on fire, people throw sand on it to put out the fire. The main use of the sand is to _________. 
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A
protect the thing on fire
B
add weigh to the thing on fire
C
keep the air away from the thing on fire
D
lower the temperature of the thing on fire
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We have two rooms to live in, but I can't decide_________. 
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A
to choose which one
B
choose which one
C
which one to choose
D
which one will I choose
---- The reading room ______ from 9a.m. to 5p.m.  ---- It’s 4 p.m. now, but the door ______.
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A
is open, is closed
B
closes, opens
C
opens, is open
D
is open, close