Yоu аre аn emergency rооm physiciаn. Marcus, a 7-year-old boy, has just presented in the ER complaining that his chest hurts, his heart feels funny, and his ankles and knees hurt. His mother says that he has had a fever for the past 24 hours. Upon physical examination, you notice that his ankles and knees are red and swollen, and examination with a stethoscope reveals unusual palpitations (his heart is fluttering). You immediately order an EKG to check for signs of a heart attack, a CBC blood draw to check for signs of infection, a throat culture to check for the presence of Streptococcus, an X-ray of his legs to check for bone fractures or lesions, and a urine sample to check for bacterial contamination.Which of the following is one of the hypotheses you have put forth?