The deflection of a uniform circular bar of diameter d and length l, which extends by an amount e under a tensile pull W, when it carries the same load at its mid-span is

A

$$ el / 2d $$ 

B

$$ (e^2 l) / (3d^2) $$

C

$$ (el^2 ) / (3d^2) $$ 

D

$$ √e / (3d^2) $$