Final answer:
The reasons for the proof in this question involve congruent corresponding angles, supplementary angles, consecutive interior angles, and identified angles.
Step-by-step explanation:
For statement A, the reason for the proof is that angles Z3 and 24 are corresponding angles and when two parallel lines are intersected by a transversal, corresponding angles are congruent.
For statement B, the reason for the proof is that supplementary angles add up to 180 degrees.
For statement C, the reason for the proof is that angles 22 and 23 are consecutive interior angles and when two parallel lines are intersected by a transversal, consecutive interior angles add up to 180 degrees.
For statement D, the reason for the proof is that angles 21 and 22 have been identified as angles.