A．Neither the Greek soldiers nor their enemy could understand the messages.
B．African soldiers shouted from tower to tower to pass messages.
C．Using flags to send messages was found by a French engineer.
D．Only by using telephone could people send speech sounds quickly.
参考答案C
解析:
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A．In a special way.
B．Over a very short distance.
C．By a musical instrument.
D．At a rather slow speed.
A．France.
B．Rome.
C．Africa.
D．America.
A．3/4 pounds.
B．4 pounds.
C．1/9 pound.
D．1/4 pounds.