If a spring extends by x on loading, then the energy stored by the spring is (if T is tension in the spring and k is spring constant)

• A

  $\frac{{\mathrm{T}}^2}{2\mathrm{x}}$

• B

  $\frac{{\mathrm{T}}^2}{2\mathrm{k}}$

• C

  $\frac{2\mathrm{x}}{{\mathrm{T}}^2}$

• D

  $\frac{2{\mathrm{T}}^2}{\mathrm{k}}$