select all of the following graphs which represent y as a function of x.

Explanation:

Step1: Recall vertical - line test

A graph represents $y$ as a function of $x$ if any vertical line drawn on the graph intersects the graph at most once.

Step2: Analyze first graph

For the first graph, any vertical line will intersect the curve at most once. So it represents $y$ as a function of $x$.

Step3: Analyze second graph

The second graph is a horizontal line. Any vertical line will intersect it at exactly one point. So it represents $y$ as a function of $x$.

Step4: Analyze third graph

In the third graph, there are vertical lines that will intersect the curve at more than one point. So it does not represent $y$ as a function of $x$.

Answer:

The first and the second graphs represent $y$ as a function of $x$.