The rule of a function is:
You CANNOT have one x-value with multiple different y values in the same function. You can however have different x values with the same y value.
Also for reference: independent means x value and dependent means y- value.
The first answer is not a function because as you can see there is one x-value with multiple y values.
second answer IS a function because as I said before you can have different x values with the same y value
third answer is a function again because you can have different x values with same y value
number four isn't a function bc again the -2 x value has 2 different y Values.