[主观题]
International trade is the exchange of goods between nations. It took place for many reasons. The first is that no nation has all of the commodities that it needs. Countries that lack some resources within their own boundaries must buy from countries that export them. Second,a country often does not have enough of a particular item to meet its needs and has to import some to satisfy its requirement. Third,one nation can sell some items at a lower cost than other countries and will also buy what it needs from those countries that have a comparative advantage in the desired items. Finally,even though a country can produce enough of an item at reasonable costs to meet its own demand,it may still import some from other countries for innovation or variety of style.