The standard deviation of $n$ observations $x_1, x_2, ....x_n$ is 2. If $ \sum_{i=1}^n x_i=20$ and $ \sum_{i=1}^n x_i^2=100$ then $n$ is $i=1$

Question

$\begin {array} {1 1} (A)\;10 \: or \: 20 & \quad (B)\;5 \: or \: 10 \\ (C)\;5 \: or \: 20 & \quad (D)\;5 \: or \: 15 \end {array}$