Question

if lines are parallel, then alternate interior angles are
complementary

supplementary

parallel

congruent

Explanation:

This is a key theorem in geometry: when two parallel lines are cut by a transversal, alternate interior angles have equal measure, meaning they are congruent. Complementary angles sum to 90°, supplementary sum to 180°, and "parallel" describes lines, not angle relationships here.

Answer:

congruent