The number of terms in the expansion of $(x+y+z)^n$ ________
$\begin{array}{1 1}(A)\;\large\frac{n+1}{2}\\(B)\;\large\frac{n+2}{2}\\(C)\;(\large\frac{n+1}{2})(\large\frac{n+2}{2})\\(D)\;\text{None of these}\end{array}$