What did the economist Milton Friedman believe that his research into the historical money supply of the United States showed? Group of answer choices The major factor in determining how the nominal GDP of the United States changed was changes in the money supply. The major factor in determining how the nominal GDP of the United States changed was changes in interest rates. The major factor in determining how the nominal GDP of the United States changed was changes in velocity, The major factor in determining how the nominal GDP of the United States changed was changes in the prices of important inputs