Task: Question Answering
Input (English): Question: In routine clinical practice, in patients infected with the human immunodeficiency virus (HIV) who are undergoing antiretroviral treatment, the laboratory tool that is used to, in the short term, know if the treatment is being effective is: 
 Options:  <1> The levels of CD4 T lymphocytes, which increase rapidly if the treatment is being effective. <2> Anti-HIV antibody levels, which decrease when a combination of antivirals is effective. <3> P24 antigenemia, which increases in effective treatments. <4> Plasma viral load (HIV RNA per ml of plasma), which decreases to undetectable levels in effective treatments. <5> The intensity of the bands observed in the Western blot, which disappear if the treatment is effective.
Output (English): 4