Answer: Affecting only future periods.
Step-by-step explanation:
From the question, we are informed that a chain of supermarkets specializing in gourmet food, that has been using the average cost method to value its inventory changed to the FIFO method in the current year.
This change should be reported on the financial statements as a retroactive effect type of an accounting change. This is necessary because it affects future period and in order to maintain comparability and consistency.