The correct answer is D) The American Revolution.
The American Revolution was a major reason why the United States changed more towards a mixed market economy.
After the Revolutionary War and within the first years of the formation of a new nation, the economy of the country was a big issue after the big debt left by the war. The United Staes stated to be a mixed economy in that the federal government and private businesses played a key role in the economic strength of the United States.
