In analyzing international trade, we often focus on a country whose economy is small relative to the rest of the world. We do so

a. because it is impossible to analyze the gains and losses from international trade without making this assumption.
b. because then we can assume that world prices of goods are unaffected by that country's participation in international trade.
c. in order to rule out the possibility of tariffs or quotas.
d. All of the above are correct.

b