Read the example given below and find out the correct choice compatible from among the alternatives:

If a professor assigns only letter grades to an exam, we know that a student who receives a grade of 'A' did better than a student who receives a 'B', but we cannot say how much better from that ordinal scale. Nor can we tell whether the difference in preference between an 'A' student and a 'B' student and a 'C' student.