This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
During inspiration when the diaphragm contracts, the intrapleural pressure becomes: 
Select and explain. 
A. More negative, B. Less negative, C. Positive, D. Equal to the intra alveolar pressure
A: More negative
Answer: A: More negative 
Explanation: The intrapleural pressure is always negative to the atmospheric pressure. During inspiration it is -6mHg and during expiration it is -2mmHg. Intrapleural pressure prevents collapse of lungs.
Intra alveolar pressure is -4mm during inspiration and +4mm Hg during expiration. It helps in flow of air in and out of alveoli and helps in exchange of gases.