Answer:
A. a good is initially produced by producers with higher opportunity costs and eventually produced by producers with lower opportunity costs
Step-by-step explanation:
The production possibility frontier is a curve that shows the two combinations of goods and services produced in an economy.
Because of trade a country can specialise in the production of goods for which it has a lower opportunity cost in its production and import goods for which it has a higher opportunity cost.
This makes the ppf bowed out as the country produces more of the good for which it has a lower opportunity cost and less of the good for which it has a higher opportunity cost.
I hope my answer helps you