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C. the United States.
D. England.
18.Old Faithful erupts
A. every 10 minutes.
B. every 60 minutes.
C. every 125 minutes.
D. every 170 minutes.
19.A geyser is
A. hot water and stream.
B. cracks and fissures.
C. hot rocks.
D. great pressure.
20.As depth increases
A. pressure increases but temperature does not.
B. temperature increases but pressure does not.
C. both pressure and temperature increase.
D. neither pressure nor temperature increases.
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