Final answer:
Virulence factors are what distinguish pathogens from non-pathogens and help them establish in the host, the correct answer is A. Virulence factors.
Step-by-step explanation:
The distinction between pathogens and non-pathogens lies in the presence of certain traits known as virulence factors. These factors include surface proteins that allow the pathogen to adhere to host cells, mechanisms to avoid the host's immune system such as antigenic variation, capsules that protect against phagocytosis, and enzymes that can break down host antibodies.
Antigens are molecules on the pathogen that the immune system recognizes, not necessarily factors that distinguish pathogens from non-pathogens or help establish the pathogen in the host. Antibodies are produced by the host in response to antigens and are not an intrinsic characteristic of the pathogen. Enzymes can be a type of virulence factor if they directly contribute to the pathogen's ability to establish itself and cause disease.
Considering these roles, the correct option that distinguishes pathogens from non-pathogens and helps establish the pathogen in the host is A. Virulence factors.