The correct answer is B.  Diagram 1 represents a miracidium, which is the stage that infects the intermediate host and diagram 2 represents a cercaria, which is the stage that infects the definitive host.  Miracidium is the free-swimming ciliated larva released from eggs produced by these parasites.  Cercaria is the infective larval form that penetrates the skin of the definitive host to develop into egg laying adult worms.