When using a thermistor, one must consider that:

A thermistor is a type of resistor whose resistance is significantly affected by temperature. This means that its resistance changes in response to environmental temperature variations, making it highly sensitive to such changes. The precise design of a thermistor allows it to measure temperatures directly by detecting the resistance changes that occur as the temperature fluctuates.

Understanding this property is crucial in applications where temperature monitoring or control is required. For example, thermistors are often used in temperature sensors, electronic thermometers, and thermal management systems.

The other choices do not accurately reflect the characteristics of a thermistor. For instance, the resistance of a thermistor does not remain constant; it varies with temperature. Additionally, being affected by electric current is not a defining characteristic of thermistors, as their primary function is to respond to temperature. Finally, while there are thermistors designed for low temperatures, they can also operate effectively over a range of temperatures, not being limited to just low temperatures. This makes the understanding of how resistance changes with environmental factors the most critical aspect when using thermistors.