Answer:
D. Country A would focus on growing carrots; country B would focus on growing apples.
Step-by-step explanation:
Country A would focus on growing carrots because the opportunity cost of producing carrots in terms of apples is 10,000 a day, which is the same for country B, but with a production of only hafl the amount of carrots.
Country B would focus on apples because doing so would only cost 20,000 carrots a day, while if Country A did so, it would cost it 40,000 carrots a day.