What are THREE ways that living conditions were so bad that they affected the public health before the 1900's.

the answer is

during longer space exploration trips, crewmembers may develop vision impairment risks and short-term cardiac atrophy or a decrease in the size, strength, weight, and activity of the heart during space flight because they can experience microgravity. in addition, the long-term medical condition is loss of bone mineral density and radiation exposure.