单项选择题
【案例分析题】
Most nations of the world export goods to other countries.Likewise，many import goods from other nations.Why do countries engage in international trade？
Firstly，some countries of the world have certain conditions that provide them with a basis for international trade.For example，Columbia and Brazil have just the right climate for growing coffee.They export the surplus to earn foreign exchange to pay for the goods they import.
Secondly，if a country has an abundance（充裕）of natural resources，it generally exports some of them.Rubber from Malaysia and oil from the Middle East countries are examples.
Thirdly，if a nation is advanced in science and technology，it can produce sophisticated（精密的）machinery and equipment，such as computers，jet airplanes and electric generators （g（发电机）.Their manufactured goods are usually sold at high prices in the international market.So they enjoy favorable conditions in the international trade.
In addition to trade in goods，there is another form.of trade，i.e.trade in service.The former is called visible trade，and the’latter，invisible trade.Transportation，insurance，financing and tourism are some of the forms of invisible trade.Trade in these forms can be as important to some nations as the exchange of goods is to others.
The word 'surplus' in the last sentence of Para.2 means（）
