You are answering a USMLE-style medical question. Question: A 47-year-old man with a history of HIV1 infection presents to his HIV clinic to discuss his antiretroviral medications. He is interested in including maraviroc in his maintenance regimen after seeing advertisements about the medication. On exam, his temperature is 98.8°F (37.1°C), blood pressure is 116/74 mmHg, pulse is 64/min, and respirations are 12/min. His viral load is undetectable on his current regimen, and his blood count, electrolytes, and liver function tests have all been within normal limits. In order to consider maraviroc for therapy, a tropism assay needs to be performed. Which of the following receptors is affected by the use of maraviroc? Options: A) gp120 B) gp160 C) p24 D) Reverse transcriptase Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.