Answer: Option D
Explanation:
A. Asking how often the customer buys the product might not give fair results as it highly depends on customers behavior and also no certain time period is considered.
B. Expenditure might not give fair results as some customers might purchase less of a product but the brand they consume is expensive than others.
C. Preference of the user is not complete information as there is no quantity and time period consideration in data.
D. In this option one is getting information about both quantity required and the time period for which it required. Hence, option D is the correct answer.