Let $x_,x_2,x_3,x_4,x_5$ be the observations with mean m and standard deviation s. The standard deviation of the observation $kx_1,kx_2,kx_3,kx_4,kx_5$ is

Question

$\begin{array}{1 1}(A)\; k+s\\(B)\;\frac{s}{k}\\(C)\;ks\\(D)\;s \end{array} $