According to the theory of comparative advantage, nations gain from trade because

A) Trade makes firms behave more competitively, reducing their market power.
B) All firms can take advantage of cheap labor.
C) Output per worker in each firm increases.
D) World output can rise when each country specializes in what its does relatively best.
E) Every country has an absolute advantage in producing something.

I put D, but the answer is E, please explain why the answer is E to me, Thank you.