Explanation: 👍🏻The correct answer is B. This patient has rheumatic fever; the sequela of an infection with Streptococcus pyogenes, also known as "strep throat." This extracellular pathogen is taken up by phagocytosing cells and killed. The bacterial debris is then displayed on the phagocyte's surface to cells of the immune system. Extracellular pathogens are presented on major histocompatibility class (MHC) II, a compound made up of 2a and 2b homogenous peptides. The short peptide displayed on the MHCII is recognized by CD4+ T cells, allowing for a targeted immune response. People with rheumatic fever have developed an immune response to a streptococcal antigen that is similar to human antigens (molecular mimicry), resulting in cross-reactivity and damage to their own tissues. Rheumatic fever is diagnosed when the Jones criteria are met. Patients must have evidence of prior S. pyogenes infection and either 2 major criteria or 1 major and 2 minor criteria. Major criteria are carditis, polyarthritis, chorea (involuntary and irregular movements of the limbs), erythema marginatum, and subcutaneous nodules. Minor criteria are arthralgia, fever; elevated ESR or CRP, and prolonged PR interval on ECG. Patients with rheumatic fever should have long-term treatment with penicillin to prevent reinfection and worsening disease.