Final answer:
The ability to detect a single drop of perfume diffused in a one-bedroom apartment is an example of an olfactory threshold, highlighting the sensitivity and complexity of the human olfactory system.
Step-by-step explanation:
The detection of a single drop of perfume diffused in an area the size of a one-bedroom apartment is an example of a(n) A) Olfactory threshold. This phenomenon can be attributed to the olfactory system which allows us to detect odorants dissolved in the nasal mucosa. Humans have numerous olfactory receptors, each responsive to different odorants, and these olfactory sensory cells transmit signals to the brain that allow us to perceive smells. This keen sensitivity to smell is due to both the high number of olfactory receptors approximately 12 million in humans and the intricate processing of olfactory information by the brain.