Answer:
A, B and C.
Step-by-step explanation:
In mathematics, a function is defined a relation between two sets, where the input set is called domain and the output set is called range.
A function has a specific rule to be defined as such. An input cannot have to different outputs. In term of diagrams, an element of the input cannot be related (with the arrow) to two different outputs values.
As you can observe in the image, relation D doesn't represents a function, because one input element relates with two output elements.
Therefore, A, B and C represent functions, because they follow the definition of function.
