Volatile molecules are sensed by olfactory receptors on the millions of hair-like cilia that cover the nasal epithelium (located in the roof of the nasal cavity). Consequently, for something to have an odour or aroma, volatile molecules must be transported in air to the nose. Volatile molecules enter the nose orthonasally during breathing/ sniffing, or retronasally via the back of the throat during eating. There are around 17,000 different volatile compounds. A particular odour may be made up of several volatile compounds, but sometimes particular volatiles (character-impact compounds) can be associated with a particular smell, e.g., iso-amyl acetate and banana/pear drops. Individuals may perceive and/or describe single compounds differently, e.g., hexenol can be described as grass, green, unripe. Similarly, an odour quality may be perceived and/or described in different compounds, e.g., minty is used to describe both menthol and carvone.

Which of the following is not mentioned as a reason that associating an odor with a specific volatile compound may be difficult?

(A) Several volatiles may contribute to producing a specific odor.
(B) People may perceive the odor of compounds differently.
(C) A character-impact compound can be associated with a particular smell.
(D) The odors of different compounds may be perceived or described as having the same quality.
(E) People may describe the odor of compounds differently.



In the context in which it appears, "volatile" most nearly means

(A) Explosive
(B) Evaporating rapidly
(C) Fleeting; transient
(D) Fluctuating rapidly
(E) Changeable