When Specialization According to Comparative Advantage Also Makes Economies of Scale

When specialization according to comparative advantage also makes economies of scale possible,

A) costs will rise in all trading countries.
B) trade is not beneficial to the country that has the absolute advantage in both goods.
C) the production possibilities boundaries of all trading countries will shift inward.
D) there will be additional gains from trade.
E) it will be beneficial for all trading countries to impose tariffs.