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

A) The vertical line test may be used to determine whether a function is one-to-one
B) A function is a relation in which each value of the input variable is paired with exactly one value of the output variable
C) A sequence is a function whose domain is the set of real numbers
D) The horizontal line test may be used to determine whether a function is one-to-one