单元整体教案NSEFCII-U02(The first period)

概要： had no knowledge of events in other places. Later, the post was introduced and horse riders carried letters. This meant that communication was further improved. Horses drawn coaches could move people from town to town in quite a comfortable way. At the beginning of the last century the steam train was invented and for the first time really fast communication became possible. Not only could le

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            had no knowledge of events in other places. Later, the post was
            introduced and horse riders carried letters. This meant that
            communication was further improved. Horses drawn coaches could move 
            people from town to town in quite a comfortable way. At the
            beginning of the last century the steam train was invented and for
            the first time really fast communication became possible. Not only
            could letters be sent easily from one part of a country to another,
            but travel was made easy, too. At about the same time, steam ships
            helped communication between countries.
            The invention of the telegraph in the middle of the last century
            further increased the speed at which messages could be sent. In this
            system electrical signals, in code, are sent along metal wires.
            These signals travel so fast that they could go nearly eight times
            round the world in one second. A special device is needed to send
            the code. At the other end another device is used in order to
            receive the code. By this method messages can be sent over distances
            of several hundred kilometres. With the invention of the telephone
            the human voice could be sent over long distances. Because of this
            the telephone system replaced the telegraph for quick communication
            over long distances. The telegraph is still used, however, by
            newspapers in order to send news and for other purposes too.
            At the beginning of this century radio was invented and in a few
            years communication was again improved. The main difference between
            radio and telephone is that radio uses no electrical signals which
            travel long distances along wires. Instead invisible waves, moving
            at the same speed as electrical signals, are used. A few years ago
            there were not many radio stations in the world. Today there are

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