Need help with Geometry

Question

devinmartin0923 · Answer

Derek wrote the following paragraph proof for the Vertical Angles Theorem:

devinmartin0923 · Answer

attachment

devinmartin0923 · Answer

The sum of angle 1 and angle 4 and the sum of angle 3 and angle 4 are each equal to 180 degrees by the definition of supplementary angles. The sum of angle 1 and angle 4 is equal to the sum of angle 3 and angle 4 by the transitive property of equality. Angle 1 is equal to angle 3 _____________________.

Which phrase completes the proof?

 by construction using a straightedge
 by the definition of a perpendicular bisector
 by the subtraction property of equality
 by the vertical angles theorem

anonymous · Answer

What do you think is the answer?

devinmartin0923 · Answer

I belive it is A, 
it is definitly not D

anonymous · Answer

Why not D? Do you know what Vertical Theorem is?

devinmartin0923 · Answer

Because I thought it was the answer and it was marked incorrect :/

anonymous · Answer

What would you do so that you would only left with <1 =<3? |dw:1439936508497:dw|