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Cave men used to ... to discuss daily activities.
Inscribing on caves can be compared to .
The first means of distance communication were .
The smoke signal is still used in the Vatican to indicate .
Pigeons were used for long distance communication due to .
Cher Ami, a homing pigeon, was awarded for her service during world war I
Pony express was used to deliver messages and newspapers .
were used at sea during the late 19th century.
In the 19th century ... was the most popular way of long distance communication.
Radio in Latin means ... .
In 1864 James Maxwell showed mathematically that could travel through free space.
In 1894 Marconi made an electric bell which went off .
In 1920 ... began.
In 1876 Alexander Bell invented ... .
Only ... could afford the telephone at first.
PSTN is ... .