Final answer:
HAART, or highly active antiretroviral therapy, used to treat HIV, involves a combination of at least three drugs to effectively manage the virus and prevent resistance.
Step-by-step explanation:
HAART, which stands for highly active antiretroviral therapy, involves the use of at least three antiretroviral drugs from different classes to prevent HIV from replicating and to protect the immune system. It's essential to use a combination of drugs because the HIV virus has a high mutation rate, which allows it to rapidly develop resistance when a single drug is used. The goal of HAART is to maintain immune function, reduce viral loads, and prevent transmission, though there is always the concern over time that the virus may become resistant. Hence, researchers continually develop new anti-HIV drugs to improve treatment efficacy and combat resistance.