Final answer:
The Federal Reserve, commercial banks, and the cash-holding public can directly affect the monetary base. The Federal Reserve and commercial banks do so through monetary policy tools, while the public can affect it by how much cash they hold.
Step-by-step explanation:
Entities that can directly affect the monetary base include the Federal Reserve and commercial banks. The cash-holding public can also affect the monetary base, but not in the direct manner in which the Federal Reserve and commercial banks can through tools like open market operations, changing reserve requirements, and changing the discount rate. While members of Congress can influence monetary policy through fiscal measures and laws, they do not have the direct means to alter the monetary base as they are not involved in the day-to-day operations of issuing currency or modifying bank reserves.
The correct answer to which entities and/or groups can directly affect the monetary base is: 1) The Federal Reserve, commercial banks, and the cash-holding public.