If `x=a(b-c),\ \ y=b(c-a),\ \ z-c(a-b)` , then the value of `(x/a)^3+(y/b)^3+(z/c)^3` is `(2x y z)/(a b c)` (b) `(x y z)/(a b c)` (c) 0 (d) `(3x y z)/(a b c)`