In paragraph 2, why does the author note that there were physiological changes when subjects opened their mouths or breathed deeply? A. To present an argument in support of the tiredness theory B. To cast doubt on the reliability of the tests that measured heart rate, muscle tension and skin conductance C. To argue against the hypothesis that yawning provides a special way to improve alertness or raise physiological activity D. To support the idea that opening the mouth or breathing deeply can affect blood oxygen levels