Which one of the following therapies combines multiple drugs to fight HIV?

The correct answer is combination therapy because it specifically involves the use of multiple antiviral drugs simultaneously to target HIV. This approach is crucial in managing HIV due to the virus's ability to mutate rapidly. By combining various classes of antiretroviral agents, combination therapy reduces the likelihood of drug resistance, enhances antiviral efficacy, and leads to better overall patient outcomes.

Monotherapy refers to the use of a single drug, which can be less effective against HIV due to the potential for resistance and insufficient viral suppression. Substitute therapy typically involves replacing one medication with another, while preventive therapy is focused on preventing disease in uninfected individuals or reducing transmission, rather than treating those already infected. Therefore, combination therapy is the most effective method for treating HIV, making it the appropriate choice.