Final answer:
The Defense Strategic Guidance is reviewed and published quadrennially, which is once every four years, to guide the strategic direction of the U.S. Department of Defense.
Step-by-step explanation:
The Defense Strategic Guidance, also known as the National Defense Strategy, is reviewed and updated on a specific schedule to address the changing global security environment and to guide the U.S. Department of Defense's strategic direction. The correct frequency at which the Defense Strategic Guidance is revised and published is Quadrennially, meaning once every four years. This is part of the broader strategic defense planning process that includes assessing threats, setting priorities, and allocating resources to meet the identified security objectives.