单项选择题

The main idea of this passage is ______.

A．a new rule for all airlines
B．the defects of electronic devices
C．a possible cause of aircraft crashes
D．effective safety measures for air flight
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单项选择题
The reason why few airlines want to impose a total ban on their passengers using electronic devices is ______.
A．they don't believe there is such a danger as radio interference
B．the harmful effect of electromagnetic interference is yet to be proved
C．they have other effective safety measures to fall back on
D．most passengers refuse to take a plane which bans the use of radio and cassette players
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