Determine Whether the Relation Defines $y$ As a Function Of $x$ Give the Domain

Multiple Choice

Determine whether the relation defines $y$ as a function of $x$ . Give the domain.
- $y=-\frac{4}{x}$

A) Function; domain $(-\infty, 0) \cup(0, \infty)$
B) Not a function; domain $(-\infty, 4) \cup(4, \infty)$
C) Not a function; domain $(-\infty, 0) \cup(0, \infty)$
D) Function; domain: $(-\infty, \infty)$