Which Federal Reserve tool is primarily used to influence long-term interest rates?

Quantitative easing is the correct choice primarily because it is a monetary policy tool used by the Federal Reserve to stimulate the economy by lowering long-term interest rates. In this process, the Federal Reserve purchases government securities and other financial assets from the market, increasing the money supply. This influx of money into the economy encourages lending and investment by decreasing long-term interest rates, which can spur economic activity.

Unlike other tools such as the discount rate or reserve requirements, which primarily impact short-term interest rates and the immediate banking environment, quantitative easing specifically targets long-term rates. By significantly expanding the Fed's balance sheet with asset purchases, the program aims to make borrowing cheaper for consumers and businesses for longer durations, thus facilitating greater economic growth following periods of economic downturn or recession.