The number of dissimilar terms in the expansion of $(x_1+x_2+.....x_n)^3$ is ?

Question

$\begin{array}{1 1}n^3 \\\large\frac{n^3+3n^2}{4} \\ \large\frac{n(n+1)(n+2)}{6} \\ \large\frac{n^2(n+1)^2}{4}\end{array}$