Final answer:
The executive departments best reflect job specialization in the executive branch, with each department led by a secretary who is an expert in that field.
Step-by-step explanation:
The part of the executive branch that best reflects job specialization is c. The executive departments. These departments are responsible for specific areas of government policy and administration. In the United States, the executive branch is made up of 15 Cabinet-level departments, such as the Department of Defense and the Department of State, as well as various agencies and bureaus. Each department is led by a secretary (with the exception of the Department of Justice, which is headed by the Attorney General), and these leaders are experts in their respective fields who advise the president and assist in implementing policies.