Ans: D. Tympanic membrane(Ref Miller's 7/e p1550)Though pulmonary aery is the gold standard site for core temperature measurement, esophagus has similar reliability and is the most commonly used site in the anesthetic practice fior temperature monitoring.Core-Temperature Monitoring:Sites for Core Temperature MeasurementGold standard site for core temperature measurementPulmonary aeryMost accurate for brain temperatureTympanic membraneBest for brain temperatureNasopharynxBest site & most commonly used for core body temperatureLower end of esophagus