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
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
单项选择题
According to the passage, static electricity can be caused by ______.
A．using home-made electrical goods
B．wearing clothes made of natural materials
C．walking on artificial floor coverings
D．copying TV programs on a computer
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