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