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 industry, has recommended that all airlines ban 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. 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 to total ban, given that many passengers want to work during flights.
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 aircrafts 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 aircrafts 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.

单选题 The passage is mainly about ______.

【正确答案】 D

【答案解析】主旨题。本题询问文章的主要内容是什么。文章首先说明对航空公司最大的威胁来自电磁干扰。接着，文章介绍了专家的建议：尤其在飞机起降期间禁止使用这些电子设备。不同的航空公司也采取了不同对策。最后，文章指出由于飞机易受到电磁的干扰，这一点也可能被恐怖分子所利用，也可能被粗心的乘客忽视。

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

单选题 Few airlines want to impose a total ban on their passengers using electronic devices because

【正确答案】 B

【答案解析】推理题。文章第三段指出“because they (the experts)have not been able to reproduce these effects in s laboratory，they have no way of knowing whether the interference might be dangerous or not.”，因此航空公司对禁止在飞机上使用电子设备表现出犹豫不决，由此可以推断出航空公司没有彻底禁止机上乘客使用电子设备的原因是电磁干扰的破坏性影响尚未得到证实。

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

【正确答案】 C

【答案解析】细节题。就为什么难以预告飞机上的电脑可能产生的电磁干扰的原因，作者在第三段给出了答案：“because they (the experts) 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.”，可见原因应是科学家尚不能在实验室中复制这种电磁影响。

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

【正确答案】 A

【答案解析】推理题。作者开篇指出“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.”可见作者对电磁干扰是非常关心的，对飞机上使用电子设备是非常忧虑的，因此也就不难推理出“作者赞成彻底禁止使用电子设备。”