单项选择题

The passage is mainly about ______.

A．a new regulation 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
Few airlines want to impose a total ban on their passengers using electronic devices because ______.
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．most passengers refuse to take a plane which bans the use of radio and cassette players
D．they have other effective safety measures to fall back on
单项选择题
Why is it difficult to predict the possible effects of electromagnetic fields on an airplane' s computers
A．Because it is extremely dangerous to conduct such research on an airplane.
B．Because it remains a mystery what wavelengths are liable to be interfered with.
C．Because research scientists have not been able to produce the same effects in labs.
D．Because experts lack adequate equipment to do such research.
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