Let a, x, y, z be real numbers such that ax−y+z=3a−1 ve x−ay+z=a2−1, which of the followings cannot be equal to x2+y2+z2?<spanclass=′latex−bold′>(A)</span>2<spanclass=′latex−bold′>(B)</span>3<spanclass=′latex−bold′>(C)</span>2<spanclass=′latex−bold′>(D)</span>34<spanclass=′latex−bold′>(E)</span>None of the preceding