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 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.

单选题 According to the passage, people started to make glass ______.
A. 4 500 years ago B. nearly 4 500 years ago
C. less than 4 500 years ago D. no less than 4 500 3,ears ago

单选题 One of the extraordinary qualities of glass is that it can carry ______.
A. light signals B. sound signals C. electric signals D. any signals

单选题 According to the passage the new telephone communication system ______.
A. has been put into actual use
B. was put into actual use in 1977
C. was put on experiment in 1977
D. had been repeatedly experimented on before 1977

单选题 Which statement can be the main idea of the passage?
A. Glass is very useful because it has unusual qualities.
B. Light signals have changed the use of glass in industry.
C. Glass fibres have reduced the cost of telephone communication.
D. The use of glass fibres to carry telephone messages is an interesting new development.