单项选择题

A high negative ion count is likely to be found ______.

A．near a pond with a water pump
B．close to a slow-flowing river
C．high in some barren mountains
D．by a rotating water sprinkler
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单项选择题
By observing the behavior of animals, scientists may be able to ______.
A．prevent disasters
B．organize groups of people
C．predict earthquakes
D．control areas of California
单项选择题
People should be able to come to a decision about ions in the air if they ______.
A．note their own reactions
B．move to a healthier area
C．observe domestic animals
D．watch how wealthy people behave
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