Fill in the blank with the phrase that makes the proof statement true.

Lines m and n are parallel. Angle 1 is congruent to angle 2 by the Corresponding Angles Postulate. Angle 1 is congruent to angle 3 because they are vertical angles. by the Transitive Property.

A. Angle 2 is congruent to angle 3

B. Angle 3 is supplementary to angle 1

C. Angle 2 is congruent to angle 1

D. Angle 1 is complementary to angle 2