Which table represents a linear function?

Table 3

A table of values x and y represents a linear function, 

if the change in x is always proportional with the change in y:

For example:

x changes from 1 to 2, y changes from -3 to -5

that is, a change of 1 in the x-es, is a change of +2 in the y's.

x changes from 2 to 4, y changes from -5 to -9
that is, a change of 2 in x, is a change of +4 in the y's.

1, 2  and 2, 4 are proportional

Another way we can check that Table 3 is the only one representing a linear function, is the constant change in y:

as x takes the values : 1, 2, 3, 4, y becomes -3, -5, -7, -9

that is, a constant change of 1 in the x-es, means a constant change of +2 in the y's