Final answer:
The text's central idea is that humans can contract dangerous diseases from animals, best supported by an instance of farm workers falling ill and some cases resulting in coma and death. Option c is correct.
Step-by-step explanation:
The central idea of the text is that humans can contract dangerous diseases after coming into contact with infected animals. This is supported by the statement which indicates that diseases can cross species barriers, potentially resulting in serious health issues for humans, as seen with diseases like avian influenza and SARS.
Part B: The quote from the text that best supports this central idea is: "Some pigs died. Tragically, farm workers also started getting sick. In severe cases, people entered a coma and died." This quote illustrates a direct instance where humans contracted a disease from animals, which had grave consequences for the affected individuals.