ANS:C - both (a) & (b)

The thermal conductivity of a conducting solid material primarily depends upon its temperature. The thermal conductivity of a material is a measure of its ability to conduct heat. In general, the thermal conductivity of most materials increases with increasing temperature, as higher temperatures lead to increased atomic and molecular vibrations, which enhance the transfer of thermal energy. Porosity, on the other hand, can affect the thermal conductivity of a material to some extent, especially in porous materials such as insulators. However, porosity is not a primary factor affecting thermal conductivity in most conducting solids. Therefore, the correct answer is: "temperature."