单选题 The biggest safety threat facing airlines today may not be a terrorist with a gun, but the man with the portable computer in business class. In the last 15 years, pilots have reported well over 100 incidents that could have been caused by electromagnetic interference. The source of this interference remains unconfirmed, but increasingly, experts are pointing the blame at portable electronic devices such as portable computers, radio and cassette players and mobile telephones.
RTCA, an organization which advises the aviation (航空) industry, has recommended that all airlines ban(禁止)such devices from being used during "critical" stages of flight particularly take- off and landing. Some experts have gone further, calling for a total ban during all flights. (76) Currently, rules on using these devices are left up to individual airlines. And although some airlines prohibit passengers from using such equipment during take- off and landing, most are reluctant to enforce a total ban, given that many passengers want to work during flights.
The difficulty is predicting how electromagnetic riel& might affect all aircraft's computers. (77)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(易受损的)to interference raises the risk that terrorists may use radio systems in order to damage navigation equipment. (78) As worrying, though, is the passenger who can't hear the instructions to turn off his radio because the music's too loud.

单选题 The main idea of this passage is ______.

单选题 What is said about the over 100 aircraft incidents in the past 15 years?

单选题 The reason why few airlines want to impose a total ban on their passengers using electronic devices is ______.

【正确答案】 B

【答案解析】[分析] 本题问：这一题考核的是对文章全篇内容的正确理解。航空安全问题涉及乘客的生命，如若事实证明使用这种设备是导致空难的原因，那么各航空公司全程禁止使用这种设备是不会遭到乘客的拒绝的，但正是这一点尚未得到证实，所以各航空公司对全程禁止使用这种设备尚犹豫不决。因此本题的答案是B项。

单选题 Why is it difficult to predict the possible effects of electromagnetic fields on an airplane's computers?

单选题 It can be guessed from the passage that the author ______.

【正确答案】 A

【答案解析】[分析] 这是一道推导出作者态度的问题。从全篇来看，作者对在飞机上全面禁止使用便携式电子设备态度是肯定的，作者对问题的提出(The biggest safety threat facing airlines today...)，列举的数据以及谈论这一问题的口气，都可以看出这一点，因此选项A是答案。