What strategy involves controlling access to a region in an operational environment?

The strategy that involves controlling access to a region in an operational environment is closely aligned with operational shielding. This strategy focuses on denying enemy access or maneuverability in specific areas, which is crucial for maintaining a tactical advantage and ensuring the security of one's own forces and objectives.

Operational shielding can involve various tactics, such as establishing physical barriers, implementing reconnaissance and surveillance measures, or leveraging intelligence to guide forces in dominating key terrain. In this context, controlling access becomes not just about physical presence but also manipulating the situational awareness and operational tempo of opposing forces.

While changing the nature of conflict and controlling tempo are certainly important strategies in military operations and can contribute to access control indirectly, they don't specifically focus on the direct aspect of access denial. The first option represents the most direct approach to achieving that strategic goal.

Therefore, the comprehensive answer “all of the above” encapsulates the broader series of strategies that together form a complete operational picture. However, operational shielding remains the fundamental strategy at the heart of controlling access in an effective manner, ensuring that the environment remains favorable for friendly forces while denying adversaries the freedom to operate.