While consumerism during the 1920s boosted the economy, it also led to
more savings.
higher debt.
lower debt.
fewer stocks.

I believe the answer is: higher debt

The increase of consumerism in 1920s is created because of the early development of credit card companies.

At that time, there is not strict regulation on credit score, which mean that even those who do not have high enough income would obtain low interest credit. This lead to a massive increase in average debt.

c is the correct answer for this question.