The correct answer is A, Metagonimus yokogawai.  Differentiation from Heterophyes and Opisthorchis may require recovery and examination of the adult worms.  Infection by the other listed parasites is not acquired by eating pickled fish.  S. japonicum produces infective cercariae that penetrate the skin to initiate infection in humans.  Fasciolopsis buski and Fasciola hepatica infections are acquired by eating certain freshwater plants contaminated with the parasite's metacercariae.

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