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  3. The making of glass is a very old industry—at least 4,500 years old. Glass has many extraordinary qualities and it is often bein

The making of glass is a very old industry—at least 4,500 years old. Glass has many extraordinary qualities and it is often bein

admin2009-03-15  30
问题     The making of glass is a very old industry—at least 4,500 years old. Glass has many extraordinary qualities and it is often being used in new ways.
    One of the most interesting new uses for glass is in telephone communication. Scientists have developed glass fibres as thin as human hair which are designed to carry light signals. When the light reaches the other end, it is first changed into electrical signals which are in turn changed into sound messages.
    Called lightwave communication, the new system was used successfully in an experiment in Chicago in 1977. During the experiment, two glass fibres were able to carry 672 conversations at the same time. The lightwave cable, containing 144 glass fibres, is able to carry 50,000 conversations at the same time.
    The lightwave communication system has two important advantages. First, the glass fibre cables are smaller and weigh less than copper cables. Second, they cost less.
    Perhaps it can be said that telephone communication has entered the age of light.
选项 A、4,500 years ago
B、nearly 4,500 years ago
C、less than 4,500 years ago
D、no less than 4,500 years ago
答案D
解析 根据第一行at least 4500 years．可知答案选D。
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