The difficulty is predicting how electromagnetic fields might affect an aircraft s computers. Experts know that portable devices 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 can t hear the instructions to turn off his radio because the music s too loud.

　　21. The passage is mainly about ________.

　　A) a new regulation for all airlines

　　B) the defects of electronic devices

　　C) a possiblecause 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.

【大学英语四级考试听力附试题和答案】相关文章：

★ 12月英语四级考试听力模拟试题十四

★ 大学英语六级考试听力的预测试卷(8)

★ 6月大学英语六级考试听力模拟训练题(17)

★ 大学英语六级考试听力的预测试卷(3)

★ 2014年英语四级考试听力之必考习语1

★ 6月英语六级听力成功指南(第二十二期)

★ 应对大学英语四级考试听力题量变化对策

★ 大学英语六级考试听力的预测试卷(4)

★ 大学英语六级考试听力模拟试题(三)

★ 12月英语六级听力重点词汇（5）