Query: What organization said Oklahoma's centennial was the top event in the US that year?
Context: Oklahoma's centennial celebration was named the top event in the United States for 2007 by the American Bus Association, and consisted of multiple celebrations saving with the 100th anniversary of statehood on November 16, 2007. Annual ethnic festivals and events take place throughout the state such as Native American powwows and ceremonial events, and include festivals (as examples) in Scottish, Irish, German, Italian, Vietnamese, Chinese, Czech, Jewish, Arab, Mexican and African-American communities depicting cultural heritage or traditions.