Answer
$b$ and $c$
Work Step by Step
The vertical line test states that a graph represents a function if any vertical line that is drawn through the graph only passes through one point in that graph.
In graph $a$, vertical lines drawn through the graph would pass through more than one point (example: $x=0$).
In graph $b$, vertical lines drawn through the graph would pass through only one point.
In graph $c$, vertical lines drawn through the graph would pass through only one point.
Therefore, only graphs $b$ and $c$ are functions.