Thermal conductivity of a material may be defined as the:

(a) Quantity of heat flowing in one second through one cubic meter of material when opposite faces are maintained at a temperature difference of \(1^{\circ} \mathrm{C}\).

(b) Quantity of heat flowing in one second through one square meter of the area and of \(1 \mathrm{~m}\) thickness of material when opposite faces are maintained at a temperature difference of \(1^{\circ} \mathrm{C}\).

(c) Both

(d) None of these