The correct answer is A. Pyrometer.
A pyrometer is a non-contact thermometer used to measure high temperatures. It works by measuring the amount of infrared radiation emitted by an object. Pyrometers are often used in metallurgical furnaces to measure the temperature of molten metals.
A thermocouple is a temperature sensor that converts temperature to an electrical voltage. It is made of two dissimilar metals that are joined together at one end. When the temperature at the junction changes, an electric current is generated. Thermocouples are often used in industrial applications to measure temperatures up to 2,000 degrees Celsius.
A thermometer is a device for measuring temperature. It is typically made of glass and contains a liquid that expands and contracts with changes in temperature. Thermometers are often used to measure human body temperature, but they can also be used to measure the temperature of other objects.
A thermistor is a type of resistor that changes its resistance with changes in temperature. Thermistors are often used in temperature sensors and thermostats.
Pyrometers are the best choice for measuring the temperature inside metallurgical furnaces because they can withstand the high temperatures. Thermocouples and thermometers are not suitable for measuring temperatures above 2,000 degrees Celsius, and thermistors are not accurate enough for measuring high temperatures.