The industry that did the most to boost other industries in the 1920s was a. aviation. b. oil refining. c. automobile making. d. steel production.

The telegraph, the transatlantic telegraph cable, and the telephone were important to businesses after 1850 because of a. they created a system for developing new inventions. b. they filled a need that other inventions of the day could not. c. they attracted investors and created the stock market. d. they made picture-taking a popular american pastime.