2. Which of the following relations is/are function/s?
a. x = {(1,2), (3,4), (1,7), (5,1)}
b. g = {(3,2), (2,1), (8,2), (5,7)
c. h = {(4,1), (2,3), (2, 6), (7, 2)}
d. y = {(2,9), (3,4), (9,2), (6,7)}​