The correct answer is C. The United States.
After the civil war, new discoveries saw the light of day. Very important contributions like products derived from steel and petroleum helped in the construction of railways and roadways.
Furthermore, great inventions for the modern era of humanity were created in the United States during this century: the telephone, the typewriter, and the gas and bulb lighting
One invention that changed the way they did business was the steam locomotive, which modernized travel and commerce.
Samuel Morse invented the Telegraph and Elias Howe the Sewing machine.