On an isosceles trapezoid, the two sides that are not parallel to each other will be exactly the same length. If this is true, than it would be create a symetric trapezoid. The diagonals would be the same length. The bases of any trapezoid are parallel, so this is true. The diagonals cannot possibly be perpendicular because the 2 nonparallel sides would be slanted. So, the answer is the 3rd choice.
