The correct answer is D. Alternate interior angles. According to the fact about the angles formed when parallel lines are cut by a transversal, angle 5 and angle 1 are corresponding angles. Corresponding angles are a pair of angles that are in the same position relative to the transversal, but on different parallel lines. In this case, angle 5 and angle 1 are on different parallel lines and are located on the same side of the transversal, hence making them alternate interior angles.
