Mammals Vary Greatly in Their Ability to Smell Odors

Mammals vary greatly in their ability to smell odors. Which property about the olfactory epithelium do you suppose is responsible for the ability of an animal to detect various odors and its sensitivity to them?

A) The number of turbinates that support the olfactory epithelium
B) The density of odorant receptor genes expressed by different populations of olfactory receptor neurons
C) The actual density of odorant receptors themselves on olfactory sensory neurons
D) The size of the olfactory epithelium
E) The number of turbinates plus the density of the odorant receptors on the olfactory sensory neurons