Answer:
A. Airplane
Explanation:
Around 1918, Air delivery, became the new mode of transportation for mail, as it rendered railroad services unnecessary. During this period, the Post Office moved on the airplane bandwagon early, there by, offering air mail service in the early 1900s.
Hence, the 1900's technological invention which allowed the U.S. postal service to deliver the mail considerably faster than previous methods is AIRPLANE.
