CQ Was Recently Exposed to Group a Hemolytic Streptococcus and Subsequently

C.Q. was recently exposed to group A hemolytic Streptococcus and subsequently developed a pharyngeal infection. His clinic examination reveals an oral temperature of 102.3° F, skin rash, and reddened throat mucosa with multiple pustules. He complains of sore throat, malaise, and joint stiffness. A throat culture is positive for Streptococcus, and antibiotics have been prescribed. The etiology of C.Q.'s disease is

A) a sore throat.
B) streptococcal infection.
C) genetic susceptibility.
D) pharyngitis.