Complex sentence: East High School has fielded the Colorado representative for the High School National Competition in 21 of the 23 year it has been contested, and is the only 5-time National winner, including victories in 3 consecutive years from 2007-2009.
Split into simpler sentences: East High School has fielded the Colorado representative for the High School National Competition in 21 of the 23 years it has been contested. It is the only 5-time National winner, including victories in 3 consecutive years from 2007-2009.