Zigbee is the correct answer because it operates on the IEEE 802.15.4 standard, which is specifically designed for low-data rate, low-power applications typically used in smart devices for automation like lighting and HVAC systems. Zigbee networks support mesh topologies, allowing extensive coverage with minimal power consumption, which is ideal for a smart office environment. While Bluetooth and Wi-Fi could also be used in IoT environments, they do not focus primarily on low-power and low-data rate operation as Zigbee does. NFC, being designed mainly for close-proximity (few centimeters) communication, is not suitable for automation environments that require extended coverage.