The correct options are option C and D, because each x values (domain) maps to a specific y values.
What is a function?
A function is a relation between two sets, where the first set is the (input) commonly known as the x-values, is assigned to a specific set (output), called the y-values.
The function notation f: x ⇒ y is used to represent a function that use a set of elements from the set x (domain) and maps these sets to a elements in the set y values. Each value of x maps a specific set of y value.
From the given options, options A and B is not a function because we have a repetition of two x values that maps to different values of y.
The correct options are option C and D, because each x values (domain) maps to a specific y values.