In the figure below, lines AB and CD intersect each other at point O. The angle pairs (∠AOD, ∠COB) and (∠AOC, ∠BOD) are called ___.
∠AOC and ∠BOD are equal and vertically opposite angles.
∠AOD and ∠BOC are equal and vertically opposite angles.
Thus, the pairs of angles are vertically opposite.