Final answer:
The function that has an inverse that is also a function (satisfies the horizontal line test) is a straight line with negative slope.
Step-by-step explanation:
The function that has an inverse that is also a function (satisfies the horizontal line test) is a straight line with negative slope. This means that option a. It is a straight line with negative slope is the correct answer.
To understand why, let's consider the horizontal line test. The horizontal line test is a test used to determine if a function is one-to-one (invertible). If a horizontal line intersects a graph more than once, then the function does not have an inverse that is also a function.
Now, for a straight line with a negative slope, every horizontal line intersects the line at only one point. This means that there are no points on the line that have more than one y-value, and therefore the function has an inverse that is also a function.