Write a question about the following article: Age of Empires III was well received by critics and reviewers. The game received an average score of 82% according to GameRankings. Age of Empires III was listed as the eighth best-selling PC game of 2005, and over two million copies of it had been  sold by May 2007. GameSpot pointed out that "Age of Empires III has some very big shoes to fill", and GameSpy remarked that it "may not redefine real-time strategy gaming, but it sets the bar so high that we will be comparing games to this for years". IGN also commented on the game, saying "Age of Empires III is a superbly balanced and polished game", and: "Discounting a few niggles in the interface, the whole presentation is rock solid." Game Revolution said that it is "as detailed as a history book, and about as much fun", while GameZone stated it is "one purchase you will not come to regret". Age of Empires III was the eighth best-selling PC game of 2005 despite its late release, and sold over 2 million copies by May 2007. It received a "Gold" sales award from the Entertainment and Leisure Software Publishers Association , indicating sales of at least 200,000 copies in the United Kingdom.

Question about the article:
How many million copies of it had been sold by May 2007?