- A Diaphragm relaxed
- B Diaphragm contracted
- C Sternum moving towards ventral and anterior direction
- D Ribs moving out
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Answer:
A
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Decrease in thoracic volume occurs during expiration, which is marked by the relaxation of the diaphragm and external intercostal muscles. During expiration, the pressure within the lungs must be higher than atmospheric pressure in order to push the air out. Relaxation of the diaphragm and external intercostal muscles leads to a decrease in thoracic volume and helps in building more pressure in the lungs. Therefore, option A is the correct answer.
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