A fan control is a:

A fan control typically operates by monitoring temperature changes and responding accordingly to maintain a desired environment. The correct choice describes a normally open temperature control that closes when the temperature rises.

In this setup, the fan control remains open under normal temperature conditions, allowing no current to flow to the fan, which prevents it from operating. Once the temperature increases beyond a preset threshold, the control closes, completing the circuit and activating the fan. This functionality is essential for cooling applications, where you want the fan to operate only when the temperature exceeds a specific limit, helping to dissipate heat and maintain a comfortable environment.

In contrast, the other options describe variations of controls that operate differently. Some may suggest controls that open rather than close under temperature rise or fall, which would not activate the fan when necessary, resulting in potential overheating. Others may describe configurations that are built to behave in a way that does not support typical fan control logic, making them less desirable for standard applications.