Which of the following is a correct statement about production possibilities frontiers?

A、An economy can produce only on the production possibilities frontier.;

B、
An economy can produce at any point inside or outside a production possibilities
frontier.;

C、An economy can produce at any point on or inside the production possibilities frontier, but not outside the frontier.;

D、An economy can produce at any point inside the production possibilities frontier, but not on or outside the frontier.