Final answer:
LoRaWAN is the most suitable protocol for IoT devices that require low power consumption, long battery life, and can transmit small amounts of data over distances of several kilometres.
Step-by-step explanation:
The protocol that is good for communication of IoT devices with restricted power and low data rates over a range of a few kilometres is C. LoRaWAN. LoRaWAN (Long Range Wide Area Network) is designed for long-range communications at a low bit rate among things (connected objects), such as sensors operated on a battery. Its characteristics are especially suited for IoT devices that require long battery life, operate on low power, and transmit small amounts of data over long distances. Unlike Bluetooth and WiFi, which are ideal for short-range communications, LoRaWAN is optimized for low power consumption and can cover a much larger area, making it a smarter choice for IoT applications that need to transmit data over several kilometres.