Which area on the map has the greatest urban population at the start of the twentieth century

The northeastern portion of the east coast, region D, had the largest urban population by the start of the Twentieth Century. The area's industrialization and increased immigration from Europe helped to make this possible. CIties such as New York, Boston, and Philadelphia were some of the major urban areas here.

geography

this is because warmer climates often don't get people sick from the flu and regions where it was often colder more people received the flu. hope this if you need more reasoning i am here to