Answer:
C. y =

Explanation:
A linear function is a straight line, with the highest degree of the function being 1. That means you are looking for the function where x is to the first power, which is just x.
And as x would be the highest degree, the only other possible term in the equation would be a constant.
In A, x is to the -1 power.
In B, x is to the 3rd power.
In C, x is to the 1st power.
In D, x is to the 2nd power.
Therefore, as x is to the power of 1 in choice C, y =
represents a linear function.