Answer:
A is a function; B, C and D are not.
Step-by-step explanation:
In other words: Identify the sole function among these relationships.
A function maps any input onto exactly one output.
If a relationship maps any input onto more than one output, it is not a function.
Thus, we eliminate B, C and D. In B, for example, we have the inputs {1, 2, 3}, where the '1' has two y-values associated with it.
On the other hand, A has the domain {-1, 0, 1, 2}, and all four inputs have exactly one associated output.
