A．The life of farmers in America in general.
B．The effect of modern ideas on the life on farms.
C．The education received by children of American farmers.
D．The difference between farmers’ life in the USA and that in other countries.

A．Because the old one could not transfer signals clearly.
B．Because the old one could not send messages quickly enough.
C．Because the old one could not send more than one message at the same time.
D．Because the old one could only send two messages along the same line simultaneously.