In the figure, the line intersecting the top vertex is parallel to the base of the triangle. Select from the drop-down menus to correctly complete the statements. Angles 3, 4, and 5 form__?__ (an cute, a right, an obtuse, a stright) angle, so the sum of the angles is 180°. Because__?__ (corresponding, alternate, alternate exterior) angles are __?__(congruent, supplementary) when two parallel lines are cut by a transversal, you can substitute m∠4 for m∠1 , and m∠5 for m∠2 , making the sum of the measures of the interior angles equal to 180°.