The question asks which graph does NOT represent $y$ as a function of $x$. A graph represents $y$ as a function of $x$ if and only if each $x$-value corresponds to at most one $y$-value. This can be tested using the vertical line test: if any vertical line crosses the graph more than once, then it is not a function.

Analyzing Each Graph:

1. Graph A: Passes the vertical line test. It is a function.
2. Graph B: Fails the vertical line test because some vertical lines intersect the graph in more than one point. This is not a function.
3. Graph C: Passes the vertical line test. It is a function.
4. Graph D: Passes the vertical line test. It is a function.

Conclusion:

Graph B does not represent $y$ as a function of $x$.

Would you like a deeper explanation of the vertical line test or further clarification? Here are some related questions to explore:

1. What is the definition of a mathematical function?
2. How does the vertical line test work?
3. Can a graph fail the horizontal line test but still be a function?
4. Why are functions important in mathematics?
5. How do we determine if a piecewise graph represents a function?

Tip: Always use the vertical line test as a quick visual tool to check if a graph represents a function!