What is the reason for step 3 of this proof? given: and bisect each other. prove: quadrilateral abcd is a parallelogram. proof: statement reason 1. and bisect each other. given 2. ae = ec be = ed definition of bisection 3. maeb = mced 4. abe cde sas criterion 5. acd cab corresponding angles of congruent triangles are congruent. 6. converse of alternate interior angles theorem 7. mbec = maed vertical angles theorem 8. bec dea sas criterion for congruence 9. dbc bda corresponding angles of congruent triangles are congruent. 10. converse of alternate interior angles theorem 11. quadrilateral abcd is a parallelogram. definition of a parallelogram a alternate interior angles theorem b. corresponding angles in congruent triangles are congruent. c. for parallel lines cut by a transversal, corresponding angles are congruent. d. vertical angles theorem e. sas criterion for congruence