If $\displaystyle\sum_{i=1}^{9} (x_i - 5) = 9$ and $ \displaystyle\sum_{i=1}^{9} (x_i - 5)^2 = 45$ then the standard deviation of the 9 items $x_1, \; x_2, .... x_9$ is :

Question

( A ) 3
( B ) 2
( C ) 9
( D ) 4