In Example 4, how many different pairs of adjacent angles are there in Fig. 2.6?

Data from Example 4

In Fig. 2.6, lines AB and CD intersect at point O. Here, ∠AOC and ∠BOD are vertical angles, and they are equal. Also, ∠BOC and ∠AOD are vertical angles and are equal.

C. A Vertical angles 0 Fig. 2.6 B D