The correct answer is A. TRUE . In intelligent vision and site planning, a protection line is a boundary-type monitoring rule used to determine whether a target enters or exits a defined space. This is consistent with the motion-analysis logic in the material, where behavior judgment is based on trajectories rather than isolated frames. The document explains that “A movement trajectory consists of positions of the centroid of a moving object in individual frames” and further states that “Tripwire crossing detection mainly involves the extraction of dynamic features of an object” such as trajectory, speed, and direction .

From an engineering viewpoint, a protection line is essentially a virtual line used to determine crossing behavior at the edge of a monitored zone. Once the moving object’s trajectory intersects that defined line, the system can judge whether the target is entering or leaving the designated area. This makes the protection line useful for event rules such as entry detection, exit detection, and boundary protection. Because the statement accurately reflects how a protection line records in-and-out movement locations using monitoring analysis, it is true.