It can be inferred that which of the following situations is likely to be most problematic

to an adherent of the "essentialist" method of pathological taxonomy？

A．A patient suffering from fever, in which the virus that is apparently responsible for the symptoms has not been isolated

B．A patient suffering from lung inflammation which, though resembling other inflammations, does not respond to any known treatments

C．A patient suffering from a genetic anomaly whose cause may be known but whose consequences remain unidentified

D．A patient infected with a variety of bacteria that is known to cause two diseases with dissimilar symptoms

E．A case of a patient with symptoms that may have arisen from two known diseases of different sources