9. How many pairs of vertical angles are formed by three coplanar lines intersecting at one point
A. three
B. four
c. six
D. nine
10. If 21 and 22 form a linear pair and 21 is a right angle, which of the following is true?
A. 21 and 22 are complementary
B. 21 and 22 are supplementary
C. 21 and 2 are vertical angles
D. 21 and 22 are not congruent​