What does an HIV blood test reveal?

A. whether a person has AIDS
B. whether antibodies for the virus are present
C. whether T cells for the virus are present
D. whether a person has engaged in risky behavior

B. whether antibodies for the virus are present

An HIV blood test reveals whether antibodies for the virus are present in the person's blood. Therefore, the correct answer is B. The test detects the presence of antibodies produced by the immune system in response to HIV infection, indicating if someone has been infected with HIV. It does not determine whether a person has progressed to AIDS or whether T cells specific to the virus are present. It also does not directly reveal whether a person has engaged in risky behavior, as the test only identifies the presence of the antibodies, not the mode of transmission.