An infectious disease is ___________ .a.caused only by bacteria b.spread from person to personc.spread from animal to animal d.caused only by viruses

An infectious disease is primarily characterized by its ability to be transmitted and caused by various pathogens, which include bacteria, viruses, fungi, and parasites. Therefore, the answer to your question involves understanding the nature of infectious diseases and their modes of transmission.

Among the options provided:

• a. caused only by bacteria: This is incorrect, as infectious diseases can be caused by bacteria, viruses, and other pathogens.
• b. spread from person to person: This is true for many infectious diseases, especially those caused by viruses and bacteria.
• c. spread from animal to animal: This is also true for diseases that involve zoonoses, where diseases are transmitted between animals or from animals to humans.
• d. caused only by viruses: Similar to option (a), this is incorrect as infectious diseases can be caused by multiple types of pathogens.

Considering these points, options (b) and (c) are true, but the most comprehensive answer concerning infectious diseases in general would relate to (b) since it applies broadly to many infectious diseases affecting humans.

In conclusion, the answer that best fits the definition of an infectious disease is b. spread from person to person.