The correct answer is D. server.
A server is a computer that is used to store and provide data to other computers. It is not a necessary component of the Internet of Things (IoT), which is a network of physical objects that are embedded with sensors, software, and other technologies for the purpose of connecting and exchanging data.
RFID (radio-frequency identification) is a technology that uses radio waves to automatically identify objects. It is often used in tracking and inventory management. Sensors are devices that detect and measure physical or environmental conditions, such as temperature, pressure, or light. Nanotechnology is the manipulation of matter on an atomic or molecular scale. It has the potential to be used in a variety of IoT applications, such as developing new sensors and materials.
In conclusion, the correct answer is D. server. The other options are all involved in the working of IoT.