Which second partial derivative is correct for f(x, y, z) = x cos(y + 2z) (A) fex = 0 (B) Syy = x cos(y + 2z) (C) $zz = -2.x cos(y +22) (D) fyz = - sin(y +22) 5. Let z = x² sin y + yery, r = u + 2