The difficulty is predicting how electromagnetic fields might affect an aircrafts computers. Experts know that portable device emit radiation which affects those wavelengths which aircraft use for navigation and communication. But, because they have not been able to reproduce these effects in a laboratory, they have no way of knowing whether the interference might be dangerous or not.
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.
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