What Triggers the Process of the Sense of Smell

What triggers the process of the sense of smell?

A) Odor molecules entering the nasal cavity bind to cilia projecting from the ends of olfactory receptor cells.
B) Chemicals in saliva trigger receptors for the olfactory nerve.
C) Odor molecules entering the nasal cavity excite the olfactory bulbs under the brain's frontal lobe.
D) Chemicals in saliva stimulate nerve fibers in the soft palate, which, in turn, synapse with neurons in the olfactory bulbs.