Which of the following statements are true regarding functions? Check all that apply.

A. A function is a relation in which multiple values of the input variable are paired with at least one of the output variable.

B. A sequence is a function whose domain is the set of rational numbers.

C. The horizontal line test may be used to determine whether a function is one-to-one.

D. The vertical line test may be used to determine whether a relation is a function.