If $\bar {x}$ is the mean of n values of x, then $\sum \limits_{i=1}^{n} (x_i -\bar{x} )$ is always equal to _______. If a has any value other than $\bar {x}$ , then $\sum \limits_{i-1}^{n} (x_i -\bar {x} )^2$ is _________ than $\sum (x_i -a)^2$

Question

$\begin{array}{1 1}(A)\; 0,less \\(B)\;1,less \\(C)\;0,greater \\(D)\;1,greater \end{array}$