Which one of the following is not necessary for perimeter security ?

Perimeter security refers to the systems and technologies used to protect the boundary of a facility. Modern perimeter security typically involves four key functions: Deterrence, Detection, Delay, and Response. Lighting (D) is essential for deterrence and visibility during night operations. CCTV (A) (Closed-Circuit Television) provides continuous surveillance, monitoring, and evidence gathering. Alarm systems (C) are necessary for the immediate detection of unauthorized intrusions. While a Water moat (B) is a physical barrier used historically in medieval fortifications, it is not a necessary or standard component of modern perimeter security. Modern physical barriers usually consist of fences, walls, or sensors, which are more practical, cost-effective, and easier to maintain than moats.