Answer:
The third diagram.
Step-by-step explanation:
When we have two parallel lines cut by a transversal, vertical angles are congruent; alternate interior angles are congruent; alternate exterior angles are congruent; corresponding angles are congruent; and same-side interior angles are supplementary.
In the first diagram, we have two angles on the same side of their respective parallel lines and the same side of the transversal. These are by definition corresponding angles. Since they are not congruent, these lines are not truly parallel.
In the second diagram, we have two angles on opposite sides of the transversal and outside the block of parallel lines. These are by definition alternate exterior angles. Since they are not congruent, these lines are not truly parallel.
In the third diagram, we have two angles inside the block of parallel lines and on the same side of the transversal. These are by definition same-side interior angles. Since they are congruent, these are parallel lines.
