Final answer:
The world's largest common market is the European Union (EU), composed of 28 nations and over half a billion people. It has a combined GDP of nearly $17 trillion and aims to eliminate barriers to the movement of goods, labor, and capital across Europe.
Step-by-step explanation:
The world's largest common market, composed of 28 nations and more than half a billion people, with a combined gross domestic product (GDP) of nearly $17 trillion, is the European Union (EU). The EU originated as a free trade association after World War II and evolved into a common market and later a full economic union. It aims to eliminate barriers to the movement of goods, labor, and capital across Europe and introduced a common currency, the euro, in the early 2000s.