Lines XY and MN intersect at point O. The four angles formed are numbered 1, 2, 3 and 4 in clockwise order starting from the angle between OX and OM.
For each of the following pairs, state the relationship between the two angles (choose exactly one of: adjacent angles, linear pair, vertically opposite angles, complementary angles, supplementary angles, none of these):
a. (a) ∠1 and ∠2
b. (b) ∠1 and ∠3
c. (c) ∠2 and ∠4
d. (d) ∠3 and ∠4