Which of the following is a responsibility of Combatant Commanders?

Combatant Commanders have specific responsibilities tailored to their roles within the military hierarchy, particularly in overseeing military operations, forces, and resources within their theaters of responsibility. One of their key responsibilities is to establish personnel policies that directly affect the service members operating under their command. This includes the management and allocation of personnel as well as setting standards for their training and deployment.

The other choices do not align with the primary responsibilities of Combatant Commanders. For instance, advising the President on defense matters is primarily the role of the Secretary of Defense and other high-ranking officials within the Department of Defense. Similarly, managing intelligence operations is generally the purview of intelligence agencies and their directors, while conducting diplomatic missions falls under the domain of the State Department and diplomats rather than military commanders. This structure ensures that military and diplomatic operations are maintained separately, allowing Combatant Commanders to focus on their military objectives.