If `x=a+m ,\ \ y=b+m ,\ \ z=c+m` , the value of `(x^2+y^2+z^2-y z-z x-x y)/(a^2+b^2+c^2-a b-b c-c a)` is (a) 1 (b) `(x+y+z)/(a+b+c)` (c) `(a+b+c)/(x+y+z)` (d) not possible to find