The introduction of which of the following most contributed to declining automobile prices during the 1920s?
a)protective tariffs
b) consumer advertisements
c) installment plans
d)assembly lines

Correct answer choice is :

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.