If an Animal Is an Herbivore, Does That Mean It

If an animal is an herbivore, does that mean it cannot have interactions with organisms other than the plants it eats?

A) No; an herbivore might also have a mutualistic relationship with, for instance, intestinal bacteria.
B) No; an herbivore could be prey in predator/prey interactions.
C) Yes; natural selection predicts a single relationship strategy will eventually emerge with the greatest fitness.
D) Both a and b are correct.