Telling functions on a graph?

Question

Because a function never assigns two output values to a single input value, its graph never has
two different points with the same ___-coordinate.

I think its y-coordinate
Is that correct?

Answer 1

It should be x-coordinate.
You can have a function that has two different points with the same y-coordinate. For example: (0,1), (1, 1) is a function.

Answer 2

u can tell if a graph is a function by using the VERTICAL LINE TEST. if u draw a vertical line on the graph and it intersects the x-axis once then it a function more than once its not a function