Questions 1 to 3 are based on this passage
The decrease in responsiveness that follows continuous stimulation (adaptation) is common to all sensory systems, including olfaction. With continued exposure to chronically present ambient odors, individuals’ perception of odor intensity is greatly reduced. Moreover, these perceptual changes can be profound and durable. It is commonly reported that following extended absences from the odorous environment, reexposure may still fail to elicit perception at the original intensity. Most research on olfactory adaptation examines relatively transient changes in stimulus detection or perceived intensity—rarely exceeding several hours and often less—but because olfactory adaptation can be produced with relatively short exposures, these durations are sufficient for investigating many parameters of the phenomenon. However, exposures to odors in natural environments often occur over far longer periods, and the resulting adaptations may differ qualitatively from short-term olfactory adaptation. For example, studies show that even brief periods of odorant stimulation produce transient reductions in receptors in the olfactory epithelium, a process termed “receptor fatigue.” Prolonged odor stimulation, however, could produce more long-lasting reductions in response, possibly involving structures higher in the central nervous system pathway.

Question 1
According to the passage, the phenomenon of olfactory adaptation may cause individuals who are reexposed to an odorous environment after an extended absence to
(A) experience a heightened perception of the odor
(B) perceive the odor as being less intense than it was upon first exposure
(C) return to their original level of perception of the odor
(D) exhibit a decreased tolerance for the odorous environment
(E) experience the phenomenon of adaptation in other sensory systems

Question 2
The passage asserts which of the following about the exposures involved in the “research on olfactory adaptation” ?
(A) The exposures are of long enough duration for researchers to investigate many aspects of olfactory adaptation.
(B) The exposures have rarely consisted of reexposures following extended absences from the odorous environment.
(C) The exposures are intended to reproduce the relatively transient olfactory changes typical of exposures to odors in natural environments.
(D) Those exposures of relatively short duration are often insufficient to produce the phenomenon of receptor fatigue in study subjects.
(E) Those exposures lasting several hours produce reductions in receptors in the olfactory epithelium that are similar to the reductions caused by prolonged odor stimulation.

Question 3
The author of the passage discusses “receptor fatigue” primarily in order to
(A) explain the physiological process through which long-lasting reductions in response are thought to be produced
(B) provide an example of a process that subjects would probably not experience during a prolonged period of odorant stimulation
(C) help illustrate how the information gathered from most olfactory research may not be sufficient to describe the effects of extended exposures to odors
(D) show how studies of short-term olfactory adaptation have only accounted for the reductions in response that follow relatively brief absences from an odorous environment
(E) qualify a statement about the severity and duration of the perceptual changes caused by exposure to chronically present ambient odors