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
The teaching of reading will be successful if______.
A．teachers can improve conditions at school for the students
B．teachers can enable students to develop their own way of reading
C．teachers can devise the most efficient system for reading
D．teachers can make their teaching activities observable
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 to produce the same effects in labs.
D．Because experts lack adequate equipment to do such research.
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