Final answer:
The Chairman of the Joint Chiefs of Staff is the senior-ranking member of the armed forces.
Step-by-step explanation:
The senior-ranking member of the armed forces is the Chairman of the Joint Chiefs of Staff (option a).
The Chairman of the Joint Chiefs of Staff is the highest-ranking military officer in the United States and serves as the principal military advisor to the President of the United States. They lead the Joint Chiefs of Staff, which is composed of representatives from the Army, Navy, Air Force, Marines, and Coast Guard. The Chairman of the Joint Chiefs of Staff is responsible for providing strategic military advice to the President and the Secretary of Defense.