The fact that aircraft may be vulnerable to interference raises the risk that terrorists may use radio systems in order to damage navigation equipment. As worrying, though, is the passenger who cant hear the instructions to turn off his radio because the musics too loud.
21. The passage is mainly about ________.
A) a new regulation for al airlines
B) the defects of electronic devices
C) a possible cause of aircraft crashes
D) effective safety measures for air flight
22. What is said about the over 100 aircraft incidents in the past 15 years?
A) They may have been caused by the damage to the radio systems.
B) They may have taken place during take-off and landing.
C) They were proved to have been caused by the passengers portable computers.
D) They were suspected to have resulted from electromagnetic interference.
23. Few airlines want to impose a total ban on their passengers using electronic devices because ________.
A) they dont 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
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