Answer: B. Pathogens.
Explanation: The word pathogens refers to external agents that are hosted in live organisms (humans, animals or vegetals), and has the property of affecting the host causing diseases or damages visible or not. Saying this, the microorganisms described in the question are pathogens.
Option A. Incorrect. Tumors are described as an abnormal growth of any group of cells of an organism.
Option C. Incorrect. Interferon is a protein released by cells of the immune system when it is time to defend the body against microorganisms.
Option D. Incorrect. Immunoglobulins are proteins created specifically for attacking an antigen (something harmful for the body). They are also part of the immune system.
