About how many workers were there in the United States in 1860?

There were about 10 million workers in the us during the 1860

Which of these is not a criticism of the concentric zone model? it does not accurately describe cities after the rise of suburban development. it only applies to cities that grew after the development of the automobile. it assumes that inner-city areas will always be repurposed instead of abandoned. it places too much importance on the traditional central business district.