Given: m || cb prove: m∠abc + m∠bac + m∠acb = 180° which statement justifies that angle xab is congruent to angle abc? corresponding angles of parallel lines cut by a transversal are congruent. vertical angles are congruent. same-side interior angles of parallel lines cut by a transversal are supplementary. alternate interior angles of parallel lines cut by a transversal are congruent.