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Is using a cell phone aboard an airplane really dangerous? More and more airline companies are expanding in-flight Wi-Fi Interne

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问题     Is using a cell phone aboard an airplane really dangerous? More and more airline companies are expanding in-flight Wi-Fi Internet service to their entire fleet. In-flight calls, however, are still prohibited. If one can surf the Web, why can’t he use the cell?
    It operates on a totally different frequency. Cell phones transmit signals at roughly the same frequencies as aircraft communications—pilot radios and radar range from below 100 to 2,000 MHz, and many phones operate at 850 MHz or 1,900 MHz. Your cell could therefore—at least theoretically—interfere with navigation. Wi-Fi, on the other hand, signals at a higher frequency— anywhere from 2,500 to 5,000 MHz—and thus won’t get mixed up with the plane’s transmissions.
    In-flight Wi-Fi works like a moving Starbucks hot spot. The plane is rigged with three antennae— two on its belly and one on top—that receive signals from towers across the country. The frequency of those transmissions, 849 MHz, is within the range of airline communications. But they don’t interfere with the plane’s navigation, since 849 MHz is a dedicated frequency that was auctioned off and bought in 2006 by Aircell, which services American, Delta, and Virgin.
    But are cell phones on planes really that dangerous, anyway? Studies analyzing the dangers of inflight cell-phone use suggest the risks are small but real. In 2003, a study by IEEE Spectrum concluded that "continued use of portable RF-emitting devices such as cell phones will, in all likelihood, someday cause an accident by interfering with critical cockpit instruments such as GPS receivers." A study produced by the Radio Technical Commission for Aeronautics in 2006 found that portable electronic devices can interfere with airplane communications and laid out testing guidelines for airlines to figure out which devices should be permitted.
    The rationale for switching off other portable electronic devices is slightly different. Even if a device doesn’t transmit a signal—think iPods, Game Boys, "anything with an on-off switch"—it still emits energy at a frequency that could, possibly, interfere with the plane’s electronics. The Federal Aviation Administration requires all such devices to be off during takeoff and landings, but you’re allowed to turn them on once you reach a cruising altitude—presumably because any interference would be minimal and temporary. There are exceptions, though, for necessary devices like hearing aids and pacemakers.
Electronic devices are allowed to be turned on during flight probably because______.
选项 A、they have no interference with plane’s communications
B、they are necessary devices to some passengers
C、the reason to switch them off is different from that of cell-phone
D、the interference they bring doesn’t last long
答案D
解析 属事实细节题。选项A犯了曲解文意的错误，文中第五段明确指出电子设备是可能对飞行造成危险的，故错误。选项B犯了偷梁换柱的错误，文章最后提出一些必要的设备是根本不需要被关闭的，何谈再次打开，故错误。选项C犯了答非所问的错误，虽然属实，但并非本题答案，故错误。文章末段倒数第二句提到，这大概是因为这些电子设备即使产生影响也很可能是很小的、暂时性的影响，故选项D符合题意。
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