In the figure, ab| |cd. ∠aeb and ∠ced are congruent __1__ . ∠aec and ∠ __2__ are congruent by the vertical angles theorem. 1. a. by the linear pair theorem. b. by the vertical angles theorem. c. because they are corresponding angles for parallel lines cut by a transversal. 2. a. aeb b. bed c. ecd d. eba