The correct answer is: B. variable f1 is an example of ordinal variable.
A nominal variable is a variable that categorizes data into mutually exclusive groups. The categories do not have a natural order. For example, gender is a nominal variable with the categories “male” and “female”.
An ordinal variable is a variable that categorizes data into mutually exclusive groups that have a natural order. For example, student grade is an ordinal variable with the categories “A”, “B”, “C”, and “D”.
In the case of student grade, the categories “A”, “B”, “C”, and “D” have a natural order. A grade of “A” is better than a grade of “B”, which is better than a grade of “C”, which is better than a grade of “D”. Therefore, variable f1 is an example of an ordinal variable.
Option C is incorrect because variable f1 does belong to one of the mentioned categories. It is an ordinal variable.
Option D is incorrect because variable f1 does not belong to both the nominal and ordinal categories. It is only an ordinal variable.