According to ADP 3-0 Operations, what element is the source of power providing morale and physical strength?

The correct choice highlights the concept of the Center of Gravity, which is crucial in military operations, as articulated in ADP 3-0 on Operations. The Center of Gravity refers to the source of power that provides an advantage in terms of morale and physical strength to a force. It embodies the aspects that are essential for achieving success in operations and serves as a point of focus for efforts and resources.

Understanding the Center of Gravity is vital for military strategists and leaders because it allows them to identify what must be protected, attacked, or neutralized to gain the upper hand in conflict. This concept emphasizes not just the tangible aspects of military strength but also the intangible factors—such as morale and cohesion—that underpin a force's effectiveness in battle.

The other options, while relevant to operational concepts, do not encompass the same definition of power in terms of morale and physical strength as clearly as the Center of Gravity does. This makes it the most appropriate choice in the context of the question.