An Economic Theory About International Trade That Is Based on the Assumption

An economic theory about international trade that is based on the assumption that there are only two countries trading two goods

A) is useless,since the real world has many countries trading many goods.
B) can be useful only in situations involving two countries and two goods.
C) can be useful in the classroom,but is useless in the real world.
D) can be useful in helping economists understand the complex world of international trade involving many countries and many goods.