In the Ricardian Model... Question 6 Answer a. the PPF is upward sloping because the more a country produces a product, the higher the demand for the other. b. the PPF is a straigt line because technologies are constant within country. c. the PPF is a straight line because technologies vary as the country changes the production mix.. d. the PPF is curved. e. the PPF does not represent the maximum the country can consume