The correct answers are A) immigrants and D) ex-farmers.
The two events or circumstances that drastically changed the demographics of larger, industrial cities were immigrants and ex-farmers.
Immigrants came to America because they were looking for a better place to live and having better opportunities to find a decent job. Sometimes those immigrants left their native countries because they were suffering persecution, or there was extreme poverty in their nations. So they arrived in large cities and the population increased there because in those cities there were many fabrics. Ex farmers that lost their jobs due to new technologies in agriculture also migrated to the larger cities and the population increased even more. The consequences of that population increment were overcrowding and lack of services for many people.
