Jonathan Miller, aged 6 years, was brought to emergency room by his parents; he was presenting with fever, severe headache, a petechial rash, stiff neck and vomiting. Jonathan had a history of recurrent sinusitis and otitis media, all caused by pyogenic bacteria and treated successfully with antibiotics. Suspecting bacterial meningitis, the attending physician began an immediate course of intravenous antibiotics and requested a lumbar puncture. Neisseria meningitidis was grown from the cerebrospinal fluid. The physician was concerned about the recurrence of infections caused by pyogenic bacteria, and he suspected an immunodeficiency. He ordered blood tests and found the serum complement profiles to have low C3, factor B, and factor H, and undetectable factor I. Which of the following explains why a factor I deficiency is associated with infections caused by pyogenic bacteria? a. Elevated levels of C3 convertase C3bBb interfere with the activation of the classical pathway of complement activation. b. Rapid turnover and consumption of C3 in the serum causes inefficient fixation of C3b on the surface of pathogens, compromising opsonization and phagocytosis. c. Factor I is an opsonin that facilitates phagocytosis. d. Factor I is a chemokine and is important for the recruitment of phagocytes. e. Factor I is required for assembly of the terminal components of the complement pathway.