Step 1: Understanding the Question.
The question asks for the ranking of the world's three biggest economies specifically in the year 2006, measured by nominal Gross Domestic Product.
Step 2: Key Fact.
In 2006, the global economic ranking by nominal GDP placed the United States first by a wide margin, followed by Japan in second place, and Germany in third place.
Step 3: Detailed Explanation.
China's economy was growing very fast through the 2000s, but in 2006 it was still smaller than Germany's economy in nominal dollar terms. China only overtook Germany to become the world's third largest economy in 2007, and later overtook Japan itself around 2010.
The UK and France both had large, developed economies in 2006, but their nominal GDP was smaller than Germany's, so neither belongs in the top three for that year.
This means option (B), which places China in the top three for 2006, is a year too early, since that shift happened only in 2007.
Options (C) and (D), which drop Japan in favour of the UK or France, are also incorrect because Japan's economy was still comfortably the world's second largest in 2006.
Step 4: Final Answer.
The three largest economies in 2006 were USA, Japan and Germany, so option (A) is correct.