单选题
The troposphere is the warmest part of the atmosphere because it _______.
A、
contains a layer of ozone gases.
B、
about 42 degrees colder than on the ground.
C、
21% oxygen by weight.
D、
less than 1% of xenon by volume
E、
about 75 degrees colder than in Interlaken
F、
is warmed by the earth’s heat.
【正确答案】
F
【答案解析】
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