$\begin{array}{1 1}(A)\;\large\frac{aL^2}{2} +\frac{bL^3}{3} \\ (B)\;\large\frac{1}{2} \bigg(\frac{aL^2}{2} +\frac{bL^3}{3}\bigg) \\(C)\;aL^2+bL^3 \\(D)\;\frac{1}{2}(aL^2+bL^3) \end{array} $