Select the correct statement about the function represented by the table.

a. it is a linear function because the difference y-x for each row is constant.
b. it is an exponential function because the y-values increase by an equal factor over equal intervals of x-values.
c. it is an exponential function because the factor between each x- and y- value is constant.
d. it is a linear function because the y-values increase by an equal difference over equal intervals of x-values.