To determine which of the given options is NOT a function, we need to know what each option represents (typically this would involve looking at mathematical relationships, inputs and outputs).
Since the actual descriptions of options 1, 2, 3, and 4 are not provided, I cannot definitively tell you which is NOT a function based on your question alone.
Could you please provide the descriptions or equations for options 1, 2, 3, and 4? Then, I will be able to help you identify which of them is not a function.