Miami is a major center, and a leader in finance, commerce, culture, media, entertainment, the arts, and international trade. In 2012, Miami was classified as an Alpha−World City in the World Cities Study Group's inventory. In 2010, Miami ranked seventh in the United States in terms of finance, commerce, culture, entertainment, fashion, education, and other sectors. It ranked 33rd among global cities. In 2008, Forbes magazine ranked Miami "America's Cleanest City", for its year-round good air quality, vast green spaces, clean drinking water, clean streets, and city-wide recycling programs. According to a 2009 UBS study of 73 world cities, Miami was ranked as the richest city in the United States, and the world's fifth-richest city in terms of purchasing power. Miami is nicknamed the "Capital of Latin America", is the second largest U.S. city with a Spanish-speaking majority, and the largest city with a Cuban-American plurality.
Try to answer this question if possible (otherwise reply "unanswerable"): What classification did the World Cities Study Group give to Miami?
Alpha−World City