Given that lines a and b are parallel, angles 1 and 5 are congruent because they are corresponding angles, and angles 1 and 4 are congruent because they are vertical angles. then, by which property are angles 4 and 5 congruent? together, these statements prove which theorem? a) transitive property of congruency; if parallel lines have a transversal, then supplemental angles are congruent. b) transitive property of congruency; if parallel lines have a transversal, then alternate interior angles are congruent. c) symmetric property of congruency; if parallel lines have a transversal, then alternate exterior angles are congruent. d) commutative property of congruency; if parallel lines have a transversal, then same side interior angles are congruent.