Answer:
C, The Secretary of Defense
Step-by-step explanation:
The Secretary of Defense is the leader and chief executive officer of the United States Department of Defense. He is appointed by the President of the United States with the approval of Congress.
Although in command of the military, the Secretary is still object to the orders of the President who is Chief of the Armed Forces.
The Secretary of Defense is in command of both operational and administrative purposes of the department's forces: the Army, Marine Corps, Navy and Air Force.