The primary objective of a CCTV system is deterrence-by making individuals aware they are being monitored, it discourages unauthorized or criminal behavior. While recording for evidence and employee monitoring are benefits, they are secondary.
A (Reducing guard costs) may be a benefit but is not the main objective.
C (Evidence collection) supports post-incident action but doesn't directly deter behavior.
D (Watching employees) is an application, not the core goal.
References:
PSP Study Guide - CCTV and Surveillance Objectives
POA Manual - Surveillance and Security System Design Principles