The correct answer here is the second answer.  In the later parts of the 19th century, there were many poor immigrants in American cities.  They lived in crowded apartment buildings called tenements.  There were not yet any skyscrapers at that time so that is not the correct answer.  Single-family housing is a home that only has one family in it, as opposed to an apartment building.  Such houses usually cost much more than it costs to live in an apartment so poorer people do not live in such homes.  Sod houses were places where people lived on the Great Plains when they were first moving out and homesteading.  Therefore, “tenements” is the right answer.