[单项选择]Roman soldiers in some places built long rows of signal towers. When they had a message to send, the soldiers shouted it from tower to tower. If there were enough towers and enough soldiers with loud voices, important news could be sent quickly over distance.
In Africa, people learned to send messages by beating on a series of large drums (鼓). Each drum was kept within hearing distance of the next one. The drum beats were sent out in a special way that all the drummers understood. Though the messages were simple, they could be sent at great speed for hundreds of miles.
In the eighteenth century, a French engineer found a new way to send short messages. In this way, a person held a flag in each hand and the arms were moved to various positions representing different letters of the alphabet (字母表). It was like spelling out words with flags and arms.
Over a long period of time, people sent messages by all these different ways. However, not until the telephone was invented i
A. people cannot sent visible information until 19th century
B. we cannot communicate without sound
C. the ways of communication are similar in different countries
D. in ancient time, enough people is necessary to send messages over distance

最新试题

• ●    临床愈合标准中哪一项是不正确的（）
• ●    马德隆（Madelung）畸形的X线表现中，哪项是错误的（）.
• ●    [判断题]任一车站或车辆段的ATS控制设备发生故障，不影响整个ATS子系统的工作。（ ）
• ●    [单选题]要坚定（），坚信中国特色社会主义是科学社会主义理论逻辑和中国社会发展历史逻辑的辩证统一，是
• ●    [判断题]《铁路旅客运输规则》第一百一十三条 旅客身体损害赔偿金的最高赔偿人民币40000元，随身
• ●    [判断题]任何磁体都具有两个磁极,当它静止不动时,总是一个磁极指南,另一个磁极指北。(易)(