Answer: Choice A (yes it is a function; one range value exists for each domain value)
Put another way, each x corresponds to exactly one output only. We do not have any repeat x values. Any input you specify, there is only one output. If for example we had the two points (3,5) and (3,7) then the input x = 3 leads to multiple outputs y = 5 and y = 7 at the same time. This example is a non-function because of this. In this case, we don't have such repeated x values so that is why we have a function.
Try graphing out the four points given. You'll notice you cannot draw a vertical line through more than one point. Therefore, this graph passes the vertical line test. The vertical line test is to see if it's possible to draw a vertical line through more than one point on the graph. If so, then the relation fails to be a function.
