Answer:
b. it's a natural thing for humans
Step-by-step explanation:
According the the section of the "carnivore's dilemma," it is a natural thing for humans to be vegetarians. The author provided some evidence by stating that many doctors believe that "humans are naturally herbivores."
Physically speaking, humans do not have sharp claws (like usual carnivores) and sharp teeth for ripping meat. So, this means that humans are not meant to be carnivores. Thus, it is just a natural thing that for humans to eat vegetables rather than meat.
So, this explains the answer.