Final answer:
The 19th and early 20th century faced significant health issues due to poor air and water quality and a lack of knowledge on disease transmission, resulting in widespread diseases like cholera and typhoid. Improvements eventually came through better sanitation, behavioral changes, and medical advancements.
Step-by-step explanation:
The top health problems of the 19th and early 20th century can be attributed primarily to b. poor air and water quality and c. a lack of understanding about the transmission of viral diseases. Issues such as respiratory problems from coal smoke, and waterborne diseases like cholera and typhoid, which claim thousands of lives due to poor sanitation, were prevalent during this time. The open sewers and lack of modern sewage systems resulted in widespread illness, as exemplified by the 1858 Great Stink in London. Improvements in public health eventually came from better sanitation facilities, behavioral changes such as hand washing and food protection, and medical advancements like the development of immunizations and antibiotics.