What is a chief responsibility of the Secretary of Defense?

The chief responsibility of the Secretary of Defense encompasses a wide range of duties central to national security, which includes overseeing military procurement, managing military operations, and advising the President on defense matters.

The oversight of military procurement ensures that the armed forces acquire the necessary equipment and technology to maintain operational readiness and effectiveness. Managing military operations entails maintaining the oversight and coordination of the various branches of the military to ensure that defense strategies are effectively implemented. Advising the President on defense matters is a critical role, as the Secretary acts as the principal defense advisor, providing expertise and recommendations on issues that affect national security.

Given that this role integrates all these responsibilities into a comprehensive framework for national defense policy and military management, selecting an option that incorporates all these facets—like the choice that includes all of the above—accurately reflects the multifaceted nature of the Secretary of Defense's duties.