填空题

The making of glass is a very old industry — at least 4,500 years old. Glass has many extraordinary (36) __________ and it is frequently being used in new ways. One of the most (37) ____________ new uses for glass is in communication. Scientists have (38) _____________ glass fibers as thin as human (39) ____________ which are designed to carry light (40) ____________. The light is first changed into (41) ____________ signals which are used to send messages by telephone. Called light-wave (42) ____________, the new system was used successfully in an (43) __________in Chicago in 1977. (44) __________________________. The light-wave cable, containing 144 glass fibers, has the capacity to carry 50,000 conversations at the same time. (45) __________________________. First, the cables are smaller and weigh less than copper. Second, cables made of glass fibers use less space and cost less than copper. (46) __________________________.