C A light emitting diode （发光二极管）, or L．E．D．, is a device that shines when electricity passes through it．But it works differently than traditional kinds of light bulbs．Light emitting diodes use less energy and last much longer than bulbs with a filament （灯丝） inside．L．E．                               D．’s are also cooler to the touch, and shine a lot brighter than they used to． Red L．E．D．’s have long been used as signal lights on electronic equipment．But now light emitting diodes also come in blue and other colors．Colored L．E．D．’s are used to show images on everything from wireless phones to huge video signs．And white L．E．D．’s are being used increasingly to replace traditional lighting systems． But all these require electricity．In poor countries, people often burn fuel to produce light．But the smoke can make people sick．So an electrical engineering professor from Canada started a project to produce L．E．       D．lighting systems for the developing world．These lights are powered by batteries that can be recharged with energy from the sun．The batteries can also be charged through other ways, such as wind power and water power． Professor David Irvine-Halliday tells the story of how he got the idea．In 1997, while climbing in the Annapurna mountains in Nepal, he saw a small school．All the children were outside．He looked through a window and saw that inside the school was dark．The school had a sign that read: 'We have no teachers．If you want to stay and teach for a few days, we would be very pleased．' Professor Irvine-Halliday says that experience had a big effect on him．Back at the University of Calgary, he was on the Internet one day．He saw a company in Japan selling bright white L．E．                           D．’s．So he built a light with some．This is how he began the Light Up the World Foundation． 48．Compared with traditional kinds of light bulbs, L．E．D．’S________． A．waste a lot of energy                    B．need shorter time to make C．shine much brighter                 D．are warmer to touch 49．According to the passage, we know that L．E．D．’s________． A．will replace all the lights            B．will be more and more popular C．will be only colored ones               D．will be only used in developing countries 50．According to the passage, we can infer that the purpose of the Light Up the World Foundation is to________． A．develop L．E．D．lighting system for the developing world B．sell bright white L．E．D．’s C．collect money for developing countries D．earn money by selling L．E．D．’s