单项选择题

The effects produced by an excess of positive ions include ______.

A．headaches and itching
B．nausea and headaches
C．itching and tiredness
D．tiredness and pains
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单项选择题
According to the passage, positive ions can be produced by ______.
A．computer display screens
B．thunderstorms
C．earthquakes
D．typhoon
单项选择题
The author will probably agree with the statement that ______.
A．ionizers don't have a positive effect on people's health
B．a feeling of well-being is accounted for only by the presence of waterfalls or fountains
C．usual animal behavior will predict the coming of a major earthquake
D．whether seismic readings are as effective as watching animal behavior in predicting an earth quake is not certain
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