单选题 The making of glass is a very old industry at least 4,500 years old. Glass has many extraordinary qualities and it is frequently being used in new ways.
One of the most interesting new uses for glass is in telephone communication. Scientists have developed glass fibers 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 converted into sound messages.
Called light wave communication, the new system was used successfully in an experiment in Chicago in 1977. During the experiment, two glass fibers were able to carry. 672 conversations at the same time. The light wave cable, containmg 144 glass fibers, has the capacity to carry 50,000 conversations at the same time.
The light wave communication system has two important advantages. First, the glass fiber 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!

单选题 One of the extraordinary qualities of glass is that it can carry ______.

单选题 Before you can hear a message on the telephone using the new system, ______.

单选题 According to the passage the new telephone communication system ______.

单选题 From the passage, you can tell that people prefer glass fiber cables to copper cables because ______.

单选题 Which of the following statements best expresses the main idea of the passage?