The correct answer is A. To provide power to essential equipment.
A UPS, or uninterruptible power supply, is a device that provides emergency power to a load when the primary power source is interrupted. UPSs are typically used to protect computers, servers, and other critical equipment from power outages and brownouts.
Option B is incorrect because UPSs do not monitor building electricity use. This is typically done by a building management system (BMS).
Option C is incorrect because UPSs do not carry messages between departments. This is typically done by a computer network or a telephone system.
Option D is incorrect because UPSs do not control lighting and power systems. This is typically done by a BMS or a building automation system (BAS).