The correct answer is c. Antibodies.
Seroconversion refers to the development and presence of detectable antibodies against a specific pathogen in a person's blood. In the case of HIV, seroconversion occurs when the body starts producing antibodies against the virus in response to infection. HIV tests are designed to detect the presence of these antibodies, which indicates that a person has been infected with the virus. Therefore, seroconversion enables HIV tests to identify whether a person has been infected with HIV.