During Young Adulthood,rigidity Gradually Develops in the Tendons and Muscles

During young adulthood,rigidity gradually develops in the tendons and muscles of the lungs,chest,and ribs,which leads to a decrease in vital capacity,defined as ____.

A) the maximum amount of air that can be contained in the lungs
B) the minimum amount of air needed to sustain life
C) the maximum amount of carbon dioxide needed to avoid death
D) the minimum amount of pressure the diaphragm needs to exert to expand the lungs