He is looking for one of his dogs.
The comparison that would best support the idea presented in this paragraph is B, "much like the process of digestion, the phagocytes 'eat' and then digest the unwanted organisms". First of all, it is necessary to know the meaning of "engulf". To engulf, according to the Collins dictionary, means to completely cover or hide something, often in a sudden way. That's why B is the best comparison. Phagocytes eat the microorganisms and then digest them.
