For (2n + 1) observations x1, –x1, x2, –x2,.....,xn, –xn and 0, where xi’s are different, let S.D. and M.D. denote standard deviation and mean deviaiton about median, then which is true
a. S.D.< M.D.
b. S.D > M.D.
c. S.D. = M.D.
d. nothing can be said in general