Correct answer choice is :
D) Assembly lines
Explanation:
We found the survey of the 1920s with an analysis of the overall production in the economy, GNP, the most complete measure of aggregate economic movement. Real GNP growth during the 1920s was comparatively rapid, 4.2 percent a year from 1920 to 1929 according to the most broadly used estimates. Original GNP per capita grew 2.7 percent per year within 1920 and 1929.
