The correct answer is C. Positive.
The temperature coefficient of resistance is a measure of how much the resistance of a material changes with temperature. Materials with a positive temperature coefficient of resistance have an increase in resistance with increasing temperature. This is the case for most metals, including the filament in a light bulb. When the filament is heated, it expands and the atoms move further apart. This increases the distance between the electrons and the nuclei, which makes it more difficult for the electrons to flow. As a result, the resistance of the filament increases.
Materials with a negative temperature coefficient of resistance have a decrease in resistance with increasing temperature. This is the case for some semiconductors, such as silicon. When a semiconductor is heated, the electrons become more mobile and the resistance decreases.
The answer A, zero, is incorrect because the resistance of a material always changes with temperature. The answer B, negative, is incorrect because the resistance of most materials increases with increasing temperature. The answer D, about 2 ohms per degree, is incorrect because this is a specific value that is not always true.