The fact that aircraft may be fragile to interference raises the risk that terrorists may use radio systems in order to damage navigation equipment. As worrying, though, is the passenger who can 't hear the instructions to turn off his radio because the music's too loud.

12. What is said about the over 100 aircraft incidents in the past 16 years？

A. They may have been caused by the damage to-the radio systems.

B. They were proved to have been caused by the passengers portable computers.

C. They were suspected to have resulted from electromagnetic interference.

D. They may have taken place during take-off and landing.

13.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 research scientists have not been able to produce the same effects in labs.

C. Because it remains a mystery what wavelengths are liable to be interfered with.

D. Because experts lack adequate equipment to do such research.

14. Few airlines want to perform 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 refused to take a plane ,which bans the use of radio and cassette players

D. they have other effective safety measures to fall back on

15. The passage is mainly about_________.

A. a possible cause of aircraft incidents