If a transversal intersects parallel lines, which pair of angles are equal and lie on alternate interior positions?

• A. Transversal line
• B. Corresponding angles
• C. Vertically opposite angles
• D. Alternate angles

Answer: (D)

When a transversal cuts two parallel lines, the angles that lie between the lines and on opposite sides of the transversal are equal. These are called alternate interior angles. Imagine two horizontal parallel lines and a diagonal line crossing them: the interior angle on the left of the transversal at the top intersection matches the interior angle on the right of the transversal at the bottom intersection. This equality comes from the parallel nature of the lines, which makes the angle the transversal forms with each line the same, and choosing opposite sides gives the alternate interior pair. For context, vertically opposite angles are equal but occur at the same intersection, while corresponding angles are equal and lie in matching positions at the two intersections, not the alternate interior ones.