Answer:
D. Marital status of college students at a university.
Explanation:
The mean, as a measure, is appropriate when we are dealing with quantitative measures, that is, the measure that we are dealing with is a number.
In this question:
Options A(age), B(number of pages) and C(income) are all quantitative, so the mean is appropriate.
In Option D, the marital status is a qualitative measure(married, dating, single), so the mean is innapropriate, and this is the answer,