A simply supported beam of span L and flexural rigidity EI carries a unit point load at its centre. What is the strain energy in the beam due to bending?
(a) $\frac{L^{3}}{16EI}$
(b) $\frac{L^{3}}{48EI}$
(c) $\frac{L^{3}}{96EI}$
(d) $\frac{L^{3}}{192EI}$