The options A, B, C represent a function, option D is not a function.
Function of ordered pairs.
The function of an ordered pairs represents the (x, y) values of the function. The domain is the value of the input (x) and the range is the value of the output.
A function is said to be a function if a domain is attached to a single range, regardless if the domain is the same, in as much it is attached to a different range, it is still a function.
But if we have two same domain that is attached to different range, then it is not a function.
From this explanation, we can conclude that:
A = is a function
B = is a function
C = is a function
D = is not a function.