Since w*x*y*z = 0, all 4 numbers are nonzero. This means that the square of each of them will be a positive number. The sum of the square of each number will also be greater than zero. (w+x+y+z)2, on the other hand, will be equal to zero because w+x+y+z = 0. A positive number is always greater than zero, so the answer is A.