Which of the following is a function?

C

Step-by-step explanation:

For any of the functions described above, the only way any of those could be functions is that there has to be a difference value for each x, unless it is the same x-value. If the x is mentioned twice, that is fine, as long as the y point is also the same. If it is different, it is not a function.

the answer is 8/21

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