Final answer:
The question related to proving congruent angles with parallel lines lacks sufficient detail to complete a two-column proof. It generally mentions a relationship between angles created by parallel lines and transversals, indicating corresponding angles might be congruent due to the Corresponding Angles Postulate.
Step-by-step explanation:
The question appears to be about geometry and involves understanding the relationships between parallel lines and transversal angles to prove corresponding angles are congruent. Unfortunately, the information provided is not sufficient to complete a two-column proof.
Some given information or figures are missing which are crucial to proving that angle 2 is congruent to angle 3 (21 is congruent to 23). Typically, in problems involving parallel lines cut by a transversal, it can be concluded that corresponding angles are equal. This is due to the fact that if two parallel lines are cut by a transversal, then each pair of corresponding angles are congruent.
Without the proper statements and reasons for a two-column proof, it is not possible to provide a step-by-step explanation to prove the statement. However, if the lines a and b are parallel, and lines x and y are also parallel, and assuming lines a and x are transversals, then angles formed at the intersections would be corresponding and thus, by the Corresponding Angles Postulate, they would be congruent. So 21 would indeed be congruent to 23. More specific information is needed to give a precise proof.