Which graph represents a function?

Option D

Step-by-step explanation:

To be a function, it must pass the vertical line test which check if at one x-value, there are 2 y-values.

Option A doesn't work because at x = 1, there are more than 1 y-values

Option B doesn't work because throughout the whole graph there are more than 2 y-values for each x-value

Option C, doesn't work because throughout the whole graph there are more than 2 y-values for each x-value

Option D, works because for every x-value, there is only one y-value

 Option D

D or the last one

Step-by-step explanation:

the other ones don't because its possible to draw vertical lines and touch 2 points.