Answer:
E) bowed out shape of the production possibilities frontier.
Step-by-step explanation:
The production possibilities frontier curve is usually has a bowed out shape because as the production of one of the products increases, the opportunity cost of producing the other product also increases.
As shown in the attached image, as the production of Y increases, the opportunity cost of producing X will also increase, giving the curve a bowed shape. The same happens to the opportunity cost of producing Y when the production of X increases.