Which of the following describes a linear function?

A linear function is characterized by a specific relationship between its input (often referred to as x) and output (often referred to as y), where this relationship can be represented by a straight line on a graph. Mathematically, a linear function can be expressed in the form (y = mx + b), where (m) represents the slope of the line and (b) is the y-intercept. The defining feature of a linear function is that it maintains a constant rate of change; for every unit increase in x, y increases by a fixed value determined by the slope (m). This results in a graph that is not curved at any point, confirming that the representation is indeed a straight line.

In contrast, functions that include squared terms will create graphs that are parabolas rather than straight lines, introducing curvature into the representation. Similarly, a function where output is always less than input does not necessarily indicate linearity; it describes a relationship that may be linear, but also could be non-linear depending on the function's structure. Lastly, a function showing exponential growth fundamentally diverges from linearity as it illustrates a rapid increase that is not consistent with a linear increase, but instead accelerates based on the properties of