Which of the following best defines a rational function?

A rational function is defined specifically as a function that can be expressed as the ratio of two polynomial functions. This means that if you have two polynomials, ( P(x) ) and ( Q(x) ), then a rational function can be written in the form ( \frac{P(x)}{Q(x)} ), where ( Q(x) ) is not equal to zero.

This definition emphasizes that both the numerator and the denominator are polynomials, which is a critical aspect of rational functions. The ratio must also ensure that the denominator does not equal zero, as this would make the function undefined at those points.

The other options do not accurately describe what constitutes a rational function. A polynomial function is a specific type of function that does not necessarily involve a ratio of two polynomials. Functions involving square roots can be rational, but they are not automatically classified as rational functions unless they fit the ratio form. A logarithmic function is fundamentally different in structure and behavior compared to rational functions. Therefore, option C captures the essence of rational functions accurately, making it the correct answer.