Then is proportional to

Question

In case of one dimensional heat conduction in a medium with constant properties, T is the temperature at position x, at time t. Then is proportional to          

      (a) $\frac{T}{x}$                                                                    (b) $\frac{\partial T}{\partial x}$ 

      (c) $\frac{\partial^{2} T}{\partial x\partial t}$                                                                 (d)  $\frac{\partial^{2} T}{\partial x^{2}}$