Determine whether x is an eigenvector of A. A = [ 2-21 (a) x = (1, 2) O x is an eigenvector. O x is not an eigenvector. (b) x = (2, 1) O x is an eigenvector. O x is not an eigenvector. (c) x = (1, -2) O x is an eigenvector. O x is not an eigenvector. (d) x = (-1, 0) O x is an eigenvector. O x is not an eigenvector