The site by which a pathogen enters the body is called:

A. Transfer through the placenta or breast milk is a form of naturally acquired passive immunity, where antibodies are passed from mother to child without the child's immune system having to produce them.
B. Inflammation is part of the innate immune response and not related to passive immunity.
C. Vaccination with an antigen involves stimulating the body to produce its own immune response, which is active immunity, not passive.
D. Administration of antiserum provides artificially acquired passive immunity, where pre-formed antibodies are given to an individual for immediate protection.
E. Tears and saliva are part of the innate immune system (first line of defense) and are not considered forms of passive immunity.

A. Plasma refers to the liquid component of blood, not tissue fluid.
B. Chyle is a specific type of lymph that is rich in fats, typically absorbed from the intestines, and not the general fluid that enters the lymphatic vessels.
C. Lymph is the correct answer. It is the fluid that forms when tissue fluid enters the lymphatic vessels. Lymph is derived from interstitial fluid and contains water, proteins, waste products, and immune cells.
D. Serum is the liquid portion of blood without clotting factors, but it is not related to the lymphatic system.