Complex sentence: Opened to the public on 1 December 1913, the first underground line in South America, the Southern Hemisphere and the Spanish-speaking world, it made Buenos Aires the 13th city in the world to have an underground transport service.
Split into simpler sentences: Opened to the public on 1 December 1913, the first underground line in South America, the Southern Hemisphere and the Spanish-speaking world. It made Buenos Aires the 13th city in the world to have an underground transport service.