Which of the following sentences are true?
a. In resistive thermometer, the change in resistance of material per unit change in temperature should be as small as possible.
b. Thermometers are semiconductors which behave as resistors with high positive temperature coefficient.
c. Thermometers are composed of metallic oxides.
d. Thermometers are used for the measurement of level flow and pressure of fluids.

Correct option is C

Thermometer:
 A thermometer is a device that measures temperature or a temperature gradient. These are composed of metallic oxides.
 Resistance thermometer transducers, also known as RTDs (resistance temperature detectors) depend on the change of resistivity of any material when the temperature changes, and this change in the resistivity causes a change of resistance.
 The change in resistance of material per unit change in temperature should be as small as possible to get high sensitivity.
 Thermistors are essentially semiconductors that behave as resistors with a high-temperature coefficient of resistance.
 The electrical resistance varies with the temperature and is usually negative, i.e. decreases with increasing temperature, unlike metals.