Complex sentence: According to the official site, the pavilion welcomed its 4 millionth visitor on September 12,2010, and on October 30,2010, Denmark Pavilion welcomed its 5.55 millionth visitor--the population size of Denmark.
Split into simpler sentences: According to the official site, the pavilion welcomed its 4 millionth visitor on September 12,2010. On October 30,2010, Denmark Pavilion welcomed its 5.55 millionth visitor--the population size of Denmark.