Which of the following organisms cause disease?

• A. Bacteria
• B. Pathogens
• C. Viruses
• D. Fungi

Answer: (B)

Pathogens are disease-causing organisms. This term specifically means any organism capable of producing illness in a host, which includes bacteria, viruses, fungi, and other microbes. The others are broader categories that include both harmless and disease-causing members, so they don’t alone specify agents that cause disease. For example, some bacteria are harmless residents, some viruses do not cause disease in all situations (and some viruses infect bacteria rather than humans), and many fungi live without causing disease in healthy individuals. So, pathogens is the best answer because it directly refers to organisms that can cause disease across different groups.