Final answer:
Biosafety levels range from D. BSL-1 (lowest risk) to BSL-4 (highest risk), with BSL-3 being appropriate for agents that pose a moderate risk and are typically indigenous.
Step-by-step explanation:
The Biosafety levels (BSLs) are a series of protections afforded to laboratory workers and the surrounding community when they are working with microbes or infectious agents. They range from BSL-1, which is the lowest risk, to BSL-4, which is the highest risk. The order from lowest risk to greatest risk is BSL-1, BSL-2, BSL-3, and BSL-4. Specifically, BSL-3 is appropriate for research with microbes or infectious agents that pose a moderate risk to laboratory workers and the community, and these agents are typically indigenous.
Each level requires a progressively greater level of biocontainment precautions. BSL-1 applies to agents that do not typically cause disease in healthy humans and involves the fewest precautions. As we move up the levels, more strict safety measures are implemented in the labs. BSL-2 is for agents that can cause human disease but are generally not serious and are treatable. BSL-3 deals with serious or potentially lethal diseases via inhalation, and therefore requires even further safety measures and equipment. Finally, BSL-4 is for the most dangerous agents that pose a high risk of life-threatening disease, for which there might not be a vaccine or treatment available.