Nigeria's major trading partners are the countries that engage in the highest volume of trade activities with Nigeria. These countries are involved in importing and exporting goods and services to and from Nigeria. Based on the options provided, the correct answer is (a) Britain, USA, Germany, and Japan. These countries are among the top exporters of goods and services to Nigeria, and Nigeria also exports to them. The United Kingdom, United States, Germany and Japan are among the largest economies in the world and have a significant influence on the global trade system. As such, Nigeria's trade relationship with these countries has a significant impact on its economy.