A function has only one y-value for each x-value. If you find a set that has an x-value used more than once, it is not a function, because that x-value is now paired with more than one y-value.
The fourth answer is the only one that has the same x-value used more than once.
Side note: Don’t worry if a y-value is used more than once. That’s totally fine. It’s all about the x-values.
When your x is in a set of absolute value sign, any number can work for x.
As with Domain, you can do the same with range. In this case, you can go from both positive infinity and negative infinity and you will always get a real number solution.
