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第二节阅读理解梯度进阶训练 （2） More than one and a half billion people around the world live without electricity. Finding better ways to bring light to the poor is the goal of researchers like David IrvineHalliday. In the late 1990s, the Canadian professor was working in Nepal when his return flight was cancelled. A delay gave him time to take a fourteenday hiking trip in the Himalayas. As he tells it, one day he looked in the window of a school and noticed how dark it was. This is a common problem for millions of children around the world—and not just at school, but also at home. Many families use kerosene oil lamps. There are many problems with these lamps. They produce only a small amount of light. They are dangerous to breathe. And they are a big fire danger, causing many injuries and deaths each year. Kerosene costs less than other forms of lighting, but it is still costly in poor countries. Professor IrvineHalliday says many people spend well over one hundred dollars a year on the fuel. When he returned to Canada, he began researching ways to provide safe, clean and affordable lighting. He began experimenting with lightemitting diodes, LEDs, at his laboratory at the University of Calgary in Alberta. As a professor of renewable energy, he already knew about the technology. Lightemitting diodes are small glass lamps that use much less electricity than traditional bulbs and last much longer. | 
