单项选择题

Which of the following is the best title for the passage

A．Positive and Negative Ions
B．Methods of the Prediction of Earthquakes
C．Ionizer: Best Way to Improve Your Health
D．Fatigue and Headache: Plagues of Positive Ions

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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

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