American cities could adjust to rapidly growing populations, because at this time: Select one
A. building codes established maximum density standards for residential neighborhoods.
B. cities planned ahead and established water purification facilities before epidemics occurred.
C. city planners laid out zones for industry, residential areas, and commercial districts.
D. tall buildings were built with steel frames so they could ‘scrape the sky.’

The rise of big steel-framed buildings in the late 19th and early 20th century allowed American towns to adapt to their rapidly expanding populations. The construction of skyscrapers, made possible by this breakthrough, greatly expanded the amount of usable area contained within the same metropolitan footprint. Steel-frame construction made it possible for buildings to rise significantly taller than those made of traditional masonry, thereby fitting more people and companies into a smaller space. Without extending the city horizontally, this vertical development was essential for controlling the rapidly growing urban population and meeting the need for housing, office space, and commercial amenities. The Flatiron Building in New York City and the Home Insurance Building in Chicago are two prominent instances of early skyscrapers