Yawning in a class with closed door usually takes place because:

Biology · NEET · NTA ExamsBreathing and Exchange of Gases

Yawning in a class with closed door usually takes place because:
  1. the teacher is explaining a boring topic
  2. increase of carbon-dioxide levels in the blood
  3. decrease in oxygen in the air within the class hall
  4. the student has not slept properly the last night

Answer

(B) increase of carbon-dioxide levels in the blood

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