Line c intersects parallel lines a and b. Which statement proves that 4 is congruent to 8?
When two parallel lines are cut by a transversal, their alternate exterior angles measure 180°.
When two parallel lines are cut by a transversal, their alternate interior angles are congruent.
When two parallel lines are cut by a transversal, their corresponding angles are congruent.
When two parallel lines are cut by a transversal, their alternate exterior angles are congruent.