Two identical rods $A$ and $B$ are of equal lengths and at the same temperature. The rod $A$ is placed at smooth surface but $B$ is placed at rough surface. If the temperature of both are raised by the same amount, then :
(a) final length of $A$ is greater than that of $B$
(b) final length of both are same
(c) final length of $A$ is lesser than that of $B$
(d) none of the above