Which table represents a linear function?

  see below (upper left)

Step-by-step explanation:

When the x-values are sequential, a linear function will have y-values that differ by the same amount.

The upper left table has y-values that differ by -2.

The upper right table has y-values that differ by 2, -6, 2. These values are not the same.

The lower left table has y-values that differ by -1, 5, -13. These values are not the same.

The lower right table has y-values that differ by 1, 3, 5. These values are not the same.*

__

The upper left table represents a linear function.

_____

* The 2nd differences are a constant 2, so this table represents a 2nd-degree polynomial.