A、A person who is awake early. B、A bird that catches the worm early in the morning. C、A plane which flies in the morning. D、A co

An "early bird" used to be a person who was awake early and began his(or her) day’s work before other people. The people, who said it, were thinking of an old saying:  It is the early bird that catches the worm. But since 1965 the Early Bird has had a different meaning. The modem Early Bird is a communications satellite in orbit round the earth.
    The use of wires to carry telephone communications and for other purposes of the same kind does not satisfy modem needs. We had to use radio.  But the radio waves that we use for these purposes--microwaves--travel in straight lines. They do not follow the curve of the earth’s surface. We can send them from one radio station to another—a relay station--where we amplify them and send them do a third station. If there is no relay station within about 50 kilometers to receive the microwaves, they will continue into space. At a certain height, some of them are sent back to earth. A powerful station several hundred kilometers from their starting point can receive them. But these are not good ways of sending the thousands of telephone, radio and television signals across the oceans.