Mackenzie wrote the following paragraph proof for the vertical angles theorem: The sum of angle 1 and angle 4 and the sum of angle 3 and angle 4 are each equal to 180° by the definition of supplementary angles. The sum of angle 1 and angle 4 is equal to the sum of angle 3 and and angle 4_. Angle 1 is equal to angle 3 by the subtraction property of equality.

Which phrase completes the proof?

A. By construction using a straight edge

B. Buy the definition of a perpendicular bisector

C. By the transitive property of equality

D. By the vertical angles theorem