Answer: A. To make them less expensive to build.
Around 1840, tenements came into use and its original purpose was to accommodate as many immigrants as possible entering the United States at that time. In order to accommodate this large number of people all at once, tall, narrow buildings called tenements were adopted. As a result of how cheap it was to build, tenements became very popular options for housing American immigrants.
These structures were made tall because the land space was very limited. Still, they were able to accommodate numerous immigrants. Before the early 1900s, more than 80,000 tenements were already constructed in New York City and these tenements housed roughly 2.3 million. Tenement buildings had an average of eight floors. Each tenement building was constructed side by side with very little space between them. The interior rooms of these structures had no ventilation and very little light could get in.