Which does not represent a function

The thing about a function is that it must map each input in its domain to a single value. So a function needs to pass the vertical line test, which is that every vertical line on the graph passes through the curve exactly zero or one time. One time means the x value is in the domain of the function, zero times means it isn't. Two or more times means it's not a function; it has failed the vertical line test.

The sideways parabola in graph B is not a function; the y axis for example, x=0, passes through it twice.

Graph B

step-by-step explanation:

b and c