Complex sentence: December 22,1915 marked formal opening of the City's first skyscraper, the Jackson Building, which is still standing today; and in 1919 Southern Bell made improvements to the phone system.
Split into simpler sentences: December 22,1915 marked formal opening of the city's first skyscraper, the Jackson Building, which is still standing today. In 1919 Southern Bell made improvements to the phone system.