阅读文章，回答41-45题：Manycountries face a somewhat more serious economic problems in the form of anunfavorable trade bal- ance (贸易逆差)with-other nations. Such an imbalance exists when the total valueof a country’s imports ex- ceeds that of its exports. For example, if a countrybuys $ 250 billion of products from other countries, yet sells only $ 100billion of its own products overseas, its trade deficit is $ 150 billion. Manyunderdeveloped nations find themselves in this position because they lacknatural resources or the industrial capacity to use these resources, and thushave to import raw materials or manufactured goods.One effect of a trade deficit is the flowof currency (货币)out of a country. In the case of an underdeveloped nation, this cancause many financial difficulties, including failure to meet debt payments andobstacles to creation of an industrial base. Even in the case of a fullydeveloped nation such as the United States, a large tradedeficit is reason for alarm. American products, made by well-paid workers in USindustries, cost more to produce than those made in places like Asia, wherelabor and material costs are much lower. Money spent on foreign products ismoney not spent on items produced by domestic industries. Whatis the passage mainly about A: Several worldwide economic problems. B: The causes and consequences of tradedeficit. C: Lack of resources in underdevelopedcountries. D: The value of exports against imports.