Remember that
The data set is a function if every element of the domain corresponds to exactly one element of the range
so
Verify each option
I ------> is a function (every element of the domain corresponds to exactly one element of the range)
II -----> is not a function (every element of the domain does not correspond to exactly one element of the range)
III ---> is a function (every element of the domain corresponds to exactly one element of the range)
IV ----> is not a function (every element of the domain does not correspond to exactly one element of the range)
therefore
The answer is
Both I and III define a y as function of x
