For two parallel lines cut by a transversal, the alternate exterior angles are congruent.

• A. They are supplementary
• B. They are congruent
• C. They are interior angles
• D. They are adjacent angles

Answer: (B)

When a transversal crosses two parallel lines, the exterior angles on opposite sides of the transversal have equal measures. This is a direct consequence of parallel lines: angles in corresponding positions created by a transversal are equal, and the alternate exterior angles occupy those corresponding positions on opposite sides. So the exterior angle outside the lines on one side of the transversal has the same measure as the exterior angle outside the lines on the other side, making them congruent.

They’re not interior angles, not adjacent, and the familiar supplementary relationship applies to interior angles on the same side, not to these exterior, opposite-side angles.