Question

The introduction of which of the following most contributed to declining automobile prices during the 1920s?

protective tariffs
consumer advertisements
installment plans
assembly lines

Answer 1

Assembly lines allowed cheap cars for the public. Assembly lines also helped hire low skilled people. They had one job which was to put one piece on the car. 

Answer 2

(D)Assembly lines.
When an item can be quickly mass produced, it will become easier to create faster. The price will drop because the supply will grow.