A thermistor:

A thermistor is indeed a type of resistor that is specifically designed to change its resistance in response to temperature variations. This property allows thermistors to be used widely in temperature sensing and measurement applications. When temperatures increase, the resistance of a thermistor can decrease (in the case of a negative temperature coefficient thermistor) or increase (in the case of a positive temperature coefficient thermistor). This change in resistance can be measured and translated into a corresponding temperature value, making it a vital component in various electronic devices, temperature sensors, and control circuits.

The other options do not accurately describe the function of a thermistor. While it is true that some materials may change resistance with humidity, this characteristic is typically associated with other types of sensors rather than thermistors. Additionally, the function of a capacitor is fundamentally different from that of a thermistor, as capacitors store electrical energy temporarily, while thermistors are purely resistive components acting in response to temperature changes. The essential characteristic that defines a thermistor is its sensitivity to temperature, which directly correlates with its ability to change resistance based on thermal conditions.