Final answer:
The end behavior of a rational function is best described by its horizontal asymptote, which the function's graph approaches as the input grows large or small in either direction.
Step-by-step explanation:
The end behavior of a rational function is described by how the function behaves as the input approaches infinity or negative infinity. In this context, the correct answer is B) Horizontal Asymptote. Horizontal asymptotes are horizontal lines that the graph of the function approaches as the input becomes very large or very small. Other options, such as holes, vertical asymptotes, and domains, describe different aspects of a function's behavior or set. A horizontal asymptote can be a horizontal line at some positive value or a horizontal line at some negative value, depending on the ratio of the degrees of the polynomial in the numerator and the denominator of the rational function.