单项选择题

What effect does excessive positive ionization have on some people

A．They think they are insane.
B．They feel rather bad-tempered.
C．They become violently sick.
D．They are too tired to do anything.
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单项选择题
Some scientists believe that_________.
A．watching animals to anticipate earthquakes is more effective than depending on seismographs
B．the unusual behavior of animals can not be trusted
C．neither watching nor using seismographs is reliable
D．earthquakes can not affect any animals
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