The valid claim in direct opposition to the headline that "The Fed should be abolished; Congress already exists to control the economy" is (C) "The Fed is just as important as Congress, as monetary policy works differently in the economy."
This statement acknowledges the importance of the Federal Reserve (the "Fed") in managing monetary policy, which is a different aspect of the economy than fiscal policy, which is controlled by Congress. The Fed is responsible for regulating interest rates, managing the money supply, and promoting financial stability, all of which play a crucial role in the economy. Therefore, the argument that Congress already exists to control the economy overlooks the important role that the Fed plays in managing monetary policy.