Final answer:
ABH substances are detected in milk, tears, and saliva, carried by antibodies like IgA, and they play a role in the immune response.
Step-by-step explanation:
ABH substances, which are related to the ABO blood group system, are detected in various bodily secretions where they can play a role in the immune response. They are specifically carried by antibodies synthesized by the mucosal immune system, including IgA and to a lesser extent IgM. These antibodies are most notably found in tears, saliva, breast milk, and other mucous secretions of the gastrointestinal, respiratory, and genitourinary tracts. IgA, which is present in higher amounts in these secretions than IgG in the blood, is crucial for trapping pathogens to prevent infection of the mucosa.
The correct answer to the original question, "Where are ABH substances detected in secretions?" is D. All of the above, as ABH substances can be found in milk, tears, and saliva.