Keaton 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 degrees _______________. 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 by the subtraction property of equality.
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Which phrase completes the proof?
by construction using a straightedge
by the definition of a perpendicular bisector
by the definition of supplementary angles.
by the vertical angles theorem

Question

Keaton 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 degrees _______________. 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 by the subtraction property of equality.
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Which phrase completes the proof?
 by construction using a straightedge 
by the definition of a perpendicular bisector
by the definition of supplementary angles.
by the vertical angles theorem

ttp · Answer

c?