What does the term 'olfactory system' refer to?

The term 'olfactory system' specifically refers to the sensory system responsible for the sense of smell. This system encompasses the olfactory receptors located in the nasal cavity, which detect airborne molecules and send signals to the brain for interpretation. These signals help identify and distinguish various odors, playing a crucial role in the perception of smells, which can influence taste, memories, and emotions.

Other systems mentioned, such as those regulating body temperature or controlling motor functions, are distinct and serve entirely different purposes. The circulatory system, which is involved in the transportation of blood, is also unrelated to the function of smell. Thus, option A clearly identifies the core function of the olfactory system within the broader context of human senses.