A spring is held between two supports and it is in its normal length. If the center is displaced by $\delta \mathrm{x}$ normal to its length, the energy stored is the spring in proportional to $(\delta \mathrm{x})^{\mathrm{n}}$ where $\mathrm{n}$ is
(a) 1
(b) 2
(c) 3
(d) 4