The <em><u>correct answer</u></em> is:
A linear function has a constant rate of change, while a non-linear function does not have a constant rate of change.
Explanation:
As the name implies, a linear function will graph as a straight line. Since it is a straight line, this means that the distance between any two consecutive points must be the same; it must go up or down the same amount between each pair of points, or it will not form a straight line.
This means that a table of a linear function will have consecutive values that either increase or decrease by the same amount.
A non-linear function, on the other hand, will <em>not </em>have these things. It will <em>not </em>graph as a straight line, and each pair of consecutive points will <em>not </em>increase or decrease by the same amount. Instead, they will increase or decrease by different amounts.