What measures do commanders use to define lines of responsibility in support of friendly forces?

The correct choice is based on the concept of movement control measures, which are essential for defining and managing the lines of responsibility in supporting friendly forces during military operations. Movement control measures encompass procedures and protocols related to the movement of troops and supplies, ensuring that forces can operate effectively within the designated areas without interfering with each other's activities. This coordination is critical for maintaining operational efficiency, reducing the risk of fratricide, and ensuring that units can conduct their missions without unnecessary delays.

Movement control measures typically include established routes, checkpoints, and zones of operations, which allow different units to understand their areas of responsibility clearly. By implementing these measures, commanders can effectively delineate where one unit's operational authority begins and ends, facilitating smoother movements and augmenting operational success.

While operations security measures focus on safeguarding sensitive information, mission command measures pertain to the command and control processes, and strategic command measures relate to overarching command structures at higher levels of warfare, none of these options address the specific issue of defining lines of responsibility for movement and coordination as effectively as movement control measures do.