A) Contraction of the diaphragm muscles
B) Decrease in the volume of the lungs
C) Movement of ribs downward and inward
D) Relaxation of the external intercostal muscles
Correct Answer: A
Solution :
Contraction of the diaphragm muscles make it flat and contraction of the external intercostal muscles causes upward and outward movement of ribcage, thus increasing the volume of lungs. As the volume increases, the pressure inside the lungs decreases, (as shown by the part 'X of the graph). This will cause the air from outside to rush inside the lungs, causing inspiration.
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