单项选择题

This passage is about a______.

A．law
B．hypothesis
C．guess
D．theory
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单项选择题
A study of thunderclouds over the North Atlantic showed that lightning occurred only when the air temperature______.
A．around the cloud was below freezing
B．around the cloud was above freezing
C．about the cloud was lower than the temperature below the cloud
D．of the cloud was above freezing
单项选择题
According to the passage, Benjamin Franklin was the first to prove that______.
A．lightning is caused by hail through supercooled clouds
B．thunderclouds are not charged with electricity
C．thunderclouds are charged with electricity
D．lightning was not an invention of the devil
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