Given: a and b are parallel and c is a transversal. prove: ∠2 ≅ ∠7 use the drop-down menus to complete the paragraph proof showing that alternate interior angles are congruent. we know that lines a and b are parallel and that line c is a transversal because that is given. we can tell that angles 2 and 5 are congruent because "blank" angles are congruent. angles 5 and 7 are congruent because "blank" angles by parallel lines cut by a transversal are congruent. therefore, angles 2 and 7 are congruent based on the "blank"here are then answers to chose from the following segment.1st, vertical, corresponding, alternate interior, alternate exterior2ent, vertical, corresponding, alternate interior, alternate exterior3erd, symmetric property, definition of substance, transitive property, corresponding angles postulate