Question

Which reason justifies step 2 in the proof

Answer 1

Answer: C. If two lines are parallel, then the alternate interior angles formed are congruent.

This is through the alternate interior angles theorem. Angles Q and T pair up as one alternate interior set of angles that are the same measure. The same thing applies to angles X and R.

The identical arrow markers on segments XQ and TR show that those segments are parallel. Segment TQ is one transversal cut (forming alternate interior angles Q and T). Segment XR is the other transversal cut (forming alternate interior angles X and R).

We could say "angle XRT" or "angle TRX" instead of "angle R", though its ideal to use shortcuts whenever possible. The same applies for the other angles as well.