The thermistors are usually made of

A thermistor (short for "thermal resistor") is a specialized type of resistor whose electrical resistance varies significantly with temperature.

To determine the correct material and property:

Material: While standard resistors are often made from carbon or metal films, thermistors are primarily made from ceramic-like semiconducting materials. These are typically sintered metal oxides (such as the oxides of manganese, nickel, cobalt, copper, or iron).

Property: The main purpose of a thermistor is to be highly sensitive to temperature changes. For the resistance to change drastically with even a small change in temperature, the material must possess a high temperature coefficient of resistivity(denoted by $$\alpha$$). Most common thermistors are NTC (Negative Temperature Coefficient), meaning their resistance drops sharply as temperature rises, though PTC (Positive Temperature Coefficient) variants also exist.

Standard metals are not used because their temperature coefficient of resistivity is relatively low, meaning their resistance doesn't change enough to act as an effective, highly sensitive temperature sensor.

Therefore, thermistors are usually made of metal oxides with a high temperature coefficient of resistivity.

Answer: Option (C)