An Officer Might Perform a Pupil Reaction Test by Shining

An officer might perform a pupil reaction test by shining a flashlight into the eyes of a motorist. What is the best explanation for why this test is appropriate for identifying impaired drivers?

A) If a pupil dilates to more than twice it's size, part of the circuitry mediating the papillary reflex can be assumed to be impaired. Because this circuitry is affected by various drugs and alcohol, it might be indicative of an impaired driver.
B) If a pupil fails to dilate in the bright light, part of the circuitry mediating the papillary reflex can be assumed to be impaired. Because this circuitry is affected by various drugs and alcohol, it might be indicative of an impaired driver.
C) If a pupil fails to constrict in the bright light, part of the circuitry mediating the papillary reflex can be assumed to be impaired. Because this circuitry is affected by various drugs and alcohol, it might be indicative of an impaired driver.
D) If the flashlight reveals the driver's eyes to be bloodshot, it might be indicative of an impaired driver.