Which relation is a function?

a.
(6, 5), (1, 1), (6, 4)

b.
(0, 1), (2, 3), (2, 5)

c.
(8, –2), (–2, 5), (6, 0)

d.
(–2, 3), (–5, 9), (–5, 3)

Mahnoor randomly selects times to walk into a local restaurant and observe the type of music being played she found that the restaurant was playing country 11 times rock & roll 17 times and blues 8 times use the observed frequencies to create a probability model for the type of music the restaurant is playing the next time mahnoor walks in.