Which body fluids allow the HIV virus to survive best due to the presence of numerous WBCs?

The correct option highlights the body fluids that are most conducive to the survival of the HIV virus, primarily due to the high concentration of white blood cells (WBCs) found in these fluids. Blood, semen, and vaginal secretions are all types of fluids that not only contain a significant number of WBCs, which are target cells for HIV, but also provide an environment that supports the virus's survival and replication.

Blood is the most studied fluid in terms of HIV transmission; it contains a variety of immune cells, including T cells, which the virus specifically infects. Semen and vaginal secretions also contain immune cells and provide a suitable medium for the virus during sexual transmission.

In contrast, the other options contain either fewer or no WBCs at levels that would support the virus effectively. For example, saliva and sweat contain very low amounts of immune cells and are not considered effective for HIV transmission. Similarly, urine and feces do not harbor the virus in a viable state due to the lack of WBCs, and skin and mucous membranes are surfaces rather than fluids. Collectively, this understanding emphasizes why blood, semen, and vaginal secretions are critical in discussions of HIV transmission and infection control.