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  3. To get from Kathmandu to the tiny village in Nepal, Dave Irvine-Halliday spent more than two days. When he arrived, he found vil

To get from Kathmandu to the tiny village in Nepal, Dave Irvine-Halliday spent more than two days. When he arrived, he found vil

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问题     To get from Kathmandu to the tiny village in Nepal, Dave Irvine-Halliday spent more than two days. When he arrived, he found villagers working and reading around battery-powered lamps equipped with light-emitting diodes, or LEDs--the same lamps he had left there in 2000.
    Irvine-Halliday, an American photonics engineer, was not surprised. He chose to use LED bulbs because they are rugged, portable, long-lived, and, extremely efficient. Each of his lamps produces a useful amount of illumination from just one watt of power.  Villagers use them about four hours each night, then top off the battery by pedaling a generator for half an hour. The cool, steady beam is a huge improvement over lamps still common in developing countries. In fact, LEDs have big advantages over familiar incandescent (白炽的)  lights as well--so much so that Irvine-Halliday expects LEDs will eventually  take over from Thomas Edison’s old lightbulb as the world’s main source of artificial  illumination.
    The dawn of LEDs began about 40 years ago, but early LEDs produced red or green glows suitable mainly for displays in digital clocks and calculators. A decade ago, engineers invented a semiconductor crystal made of an aluminum compound that produced a much brighter red light. Around the same time, a Japanese engineer developed the first practical blue LED. This small advance had a huge impact because blue, green, and red LEDs can be combined to create most of the colors of the rainbow, just as that in a color television picture.
    These days, high-intensity color LEDs are showing up everywhere such as the traffic lights. The reasons for the rapid switchover are simple. Incandescent bulbs have to be replaced annually, but LED traffic lights should last five to yen years. LEDs also use 80 to 90 percent less electricity than the conventional signals they replace. Collectively, the new traffic lights save at least 400 million kilowatt-hours a year in the United States.
    Much bigger savings await if LEDs can supplant Mr. Edison’s bulb at the office and in the living room. Creating a white-light LED that is energy-saving, cheap and appealing has proved a tough engineering challenge. But all the major lightbulb makers--including General Electric, Philips, and Osram-Sylvania--are teaming up with semiconductor manufacturers to make it happen.
The author implies that villagers liked LED bulbs very much, because they ______.
选项 A、were given by Irvine-Halliday
B、are rugged
C、are cheap
D、are easily-recharged
答案D
解析 这是一道引申判断题。第二段提到，村民们每晚用电4个小时，然后用脚踏的方式来给电池充电。可以想象，在一个遥远的小村庄，这可能是最理想的充电方式了。
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