Answer:
The correct answer is C. pathogens.
Pathogens are microorganisms, such as bacteria, viruses, fungi, or parasites, that can cause diseases in humans, animals, or plants. They enter the body through various means, such as inhalation, ingestion, or contact with contaminated surfaces, and can cause a range of illnesses, from mild infections to life-threatening diseases. Some examples of pathogens include the influenza virus, Salmonella bacteria, and the malaria parasite. Pathogens can spread through various means, such as person-to-person contact, contaminated food or water, or exposure to infected animals.