In the 1880s many people started crowding into large cities so they could get jobs in the factories. What did the cities have to do to limit outbreaks of diseases? (A) They insisted everyone wear masks.
(B) They posted pictures of how to wash your hands in the bathrooms, and cleaned the bathrooms several times a day.
(C) They blocked people from moving into the cities by locking the city gates at night.
(D) They instituted public health and sanitation projects