Answer:
D. Vertical Angles Theorem
Step-by-step explanation:
Vertical angles theorem posits that when two straight line crosses each other, the two pairs of opposite angles which are vertical to each other are always congruent and are of equal measure.
In the diagram given, two straight line intersects at a point forming two pairs of opposite vertical angles, "angle 2 and angle 4", and "angle 1 and angle 3". These opposite vertical angles, according to the vertical angles theorem are congruent and has equal measures.
