Concept:A price index measures the average change in the price level over time, which shows how the purchasing power or value of money changes.
Explanation:A price index compares the current price level with a base year price level.
When the price level rises, the value of money falls because each unit of money buys fewer goods and services.
When the price level falls, the value of money rises.
So, a price index is used to track changes in the value or purchasing power of money over time.
It does not measure the volume of currency in the economy, the exchange rate, or the composition of goods and services.
Answer:A. how the value of money changes over time