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

Lines A and B are parallel. _ because they form a linear pair.

A. Angle 1 is supplementary to angle 2
B. Angle 1 is congruent to angle 3
C. Angle 3 is supplementary to angle 2
D. Angle 2 is congruent to angle 3

Disclaimer!! I am just figuring this our based on common sense! I do not know the correct procedure to figure it out. I still trust that it is correct though.

Lines A and B are parallel. Angle 1 is supplementary to angle 2 because they form a linear pair.

Step-by-step explanation:  

I don't know how to explain it.

c is the final answer! : )