Paul Krugman Showed That in the Case of Increasing Returns

Paul Krugman showed that in the case of increasing returns to scale and imperfect competition:

A) countries can no longer gain from international trade and would be better off making everything themselves.
B) countries gain from international trade.
C) some countries increase national welfare from trade but others lose welfare from trade.
D) countries will trade but they will gain less than in the case of the standard PPF/indifference curve model with increasing costs.