Based on the graph attached below, we can observe there is a sharp increase from the 1850s. The reason behind that increase is the Act of Consolidation in 1854, which the borders until that time expanded and resulted with the modern borders of Philadelphia. Indeed, the correct answer is an increase in the number of housing unit.
French Chemist, Louis Pasteur, and he made the vaccine for cowpox
Nuclear fear led to a new market for fallout shelters. Home economics classes taught girls how to stock such a shelter with food and supplies in the event of a nuclear attack. The government created official films on shelters, praising their value and advising homeowners on how to use them.
