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 sequence is a function whose domain is the set of real numbers. c. a function is a relation in which each value of the input variable is paired with exactly one value of the output variable. d. the horizontal line test may be used to determine whether a function is one-to-one.

The answer o this question would be: 
A.The vertical line test may be used to determine whether a function is one-to-one
D. The horizontal line test may be used to determine whether a function is one-to-one.

Vertical and horizontal line test can be used to find out whether the function, not one-to-one. The test is done by making a horizontal line (for horizontal line test) or vertical line( for vertical line test). If there are no 2 or more points of the graph that touch the line in both tests, then the function would be one-to-one