This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
75% respiration is due to: 
Select and explain. 
A. Diaphragm, B. Internal intercostals, C. Intercostals, D. Serratus anterior
A: Diaphragm
Answer: A: Diaphragm 
Explanation: Ans. A DiaphragmRef: Snell Anatomy, 7h ed. pg 499; BDC 6th ed. vol. I pg. 212-13* Diaphragm is major respiratory muscle* Inspiration is an active process and requires contraction of inspiratory muscles.* During quiet breathing expiration is a passive process.* During inspiration all the 3 dimensions of the thoracic cavity expand# Vertical-75% (by diaphragm)# AP 25% (external intercostals and internal intercostals)# Transverse# Increase in vertical diameter is brought about by downward movement of diaphragm--which account for 70% of the thoracic expansion.