TOEFL Listening: TPO-TOEFL阅读TPO - 21Z53YF1QQA3D8YLN$

In paragraph 1, what point does the author make about the evidence for the tiredness theory of yawning? A. There is no scientific evidence linking yawning with tiredness. B. The evidence is wide-ranging because it covers multiple age-groups. C. The evidence is reliable because it was collected over a long period of time. D. The evidence is questionable because the yawning patterns of children and adults should be different.