Final answer:
A graph that represents a linear function is characterized by a straight line, which can slope upward or downward, or be horizontal, depending on the value of the slope component 'b' in the equation y = a + bx. The figure labeled as (a) would be the correct representation of a linear function.
Step-by-step explanation:
The question posed appears to be focused on identifying which graph represents a linear function. A linear function can be described mathematically by a linear equation of the form y = a + bx. This indicates that when graphed, the result is a straight line which displays a direct relationship between two variables. For a linear function, if b > 0, the line will slope upward to the right, if b = 0, the line will be horizontal, and if b < 0, it will slope downward to the right.
The other graphs mentioned, such as quadratic, inverse, and exponential, do not represent linear functions as they do not produce straight lines when graphed. Therefore, a graph representing a linear function would be depicted as a straight line on a Cartesian coordinate system, regardless of the slope or y-intercept (a value). In referencing the options provided, the graph marked as (a) in Figure 1.28 is the linear graph.