Answer: I think the answer is A
Explanation:
An Outlier is any number that doesn't "Match" with the rest. In this case, the data points range from 3-13. However, most points are between 3-8. The point on the 13 seems to be out of place especially considering that the range between 3-8 is 5. Even though the range is also the same between 8-13, the problem says "outlier" in the singular form. Therefore, my answer is A.