Final answer:
The largest subunit of the executive branch is the 'department (option d),' which is part of a large bureaucratic structure including Cabinet-level departments and numerous agencies. Departments like the Department of Defense and the Department of State are headed by secretaries reporting to the president, and they have a hierarchical organizational structure.
Step-by-step explanation:
The largest subunit of the executive branch is the department. The United States executive branch includes 15 Cabinet-level departments, each headed by a secretary who reports directly to the president (except for the Department of Justice, which is led by the Attorney General). These departments are part of a large bureaucratic structure that also encompasses over 60 government agencies and various other subunits or bureaus.
Departments like the Department of Defense and the Department of State have numerous levels of bureaucracy with a hierarchical pattern of organizational structure. They consist of undersecretaries, assistant secretaries, deputy secretaries, and offices that help carry out their mission-oriented functions effectively. The president's cabinet comprises the vice president and the heads of these executive departments, with additional independent executive agencies and regulatory agencies also playing significant roles in the bureaucracy.