It is given that ab is parallel to cd and points e g h f are collinear. agf and egb are vertical and congruent by the vertical angles theorem. egb and ehd are congruent according to the finally, by the transitive property of equality

a) corresponding angles theorem; agf and ehd are congruent

b) alternate exterior angles theorem; egb and ehd are congruent

c) corresponding angles theorem; egb and ehd are congruent

d) alternate exterior angles theorem; agf and ehd are congruent