Concept:Understanding the properties of different index numbers: Laspeyres, Paasche, and Fisher.Explanation:• Paasche's index uses current year quantities, not base year quantities. So option A is false.• Fisher's index is the geometric mean (not arithmetic mean) of Laspeyres and Paasche indices. So option B is false.• The geometric mean is generally considered the most appropriate average for constructing index numbers due to satisfying reversal tests, not arithmetic mean. So option C is false.• Fisher's index satisfies both time reversal and factor reversal tests, making it an ideal index number. So option D is true.Answer:Option D is correct.