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.

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.