$\begin{array}{1 1}(A)\;\large\frac{1}{4}\normalsize n^2(n+1)^2-n&(B)\;\large\frac{1}{4}\normalsize n^2(n+1)^2+n\\(C)\;\large\frac{1}{4}\normalsize n^2(n-1)^2-n&(D)\;\large\frac{1}{4}\normalsize n^2(n-1)^2+n\end{array} $