Olfactory Neurons Have the Capacity to Regenerate in Adulthood, While

Olfactory neurons have the capacity to regenerate in adulthood, while brain neurons do not. Why is it thought olfactory neurons adapted this function?

A) As a reaction to an increasingly complex olfactory environment
B) As a response to the hazards of the olfactory environment
C) As a response to declining of air quality
D) To compensate for losses of other senses as we age