The weighted A.M of first $n$ natural numbers whose weights are equal is

Question

$\begin {array} {1 1} (A)\;\large\frac{n+1}{2} & \quad (B)\;\large\frac{2n+1}{2} \\ (C)\;\large\frac{2n+1}{3} & \quad (D)\;\large\frac{(2n+1)(n+1)}{6} \end {array}$