Which relations represent a function?

a.
(16, 14)
(14, −12 )
(9, 11)
(10, 14)

b.
(10, 8)
(7, 9 )
(9, 13)
(8, 5)

c.
(18, 24)
(16, 10 )
(5, 13)
(18, 14)

d.
(14, 12)
(10, 12 )
(−13, 7)
(11, 15)

Which term best describes the association between variables a and b? no association a negative linear association a positive linear association a nonlinear association a scatterplot with an x axis labeled, variable a from zero to ten in increments of two and the y axis labeled, variable b from zero to one hundred forty in increments of twenty with fifteen points in a positive trend.