Answer:
A. 4/5 of a banana
Step-by-step explanation:
Given that a country produces only apples and bananas.
Moving from point A to point B along its production possibilities frontier, 5 apples are gained and 4 bananas are forgone
i.e. preferences for 5 apples are equal to 4 bananas
5 apples = 4 bananas
Let us calculate unit rate i.e. how much 1 apple is equivalent to. this would give the opportunity cost, namely the cost of gain of 1 apple
1 apple= banana
Hence opportunity cost = 4/5
i.e. Option A is right