A rod of length l tapers uniformly from a diameter D at one end to a diameter D/2 at the other end and is subjected to an axial load P. A second rod of length l and of uniform diameter D is subjected to the same axial load P. Both the rods are of same material with Young's modulus of elasticity E. The ratio of extension of the first rod to that of the second rod is
(a) 4 (b) 3 (c) 2 (d) 1