Given that e parallel f and g is a transversal, we know that Angle 4 Is-congruent-to Angle 5 by the alternate interior angles theorem. We also know that Angle 1 Is-congruent-to Angle 4 and Angle 5 Is-congruent-to Angle 8 by the . Therefore, Angle 1 Is-congruent-to Angle 8 by the substitution property. A)corresponding angles theorem B)alternate interior angles theorem C)vertical angles theorem D)alternate exterior angles theorem