Lung regulates air pressure

Analysis of test questions: the contraction and relaxation of respiratory muscles cause regular expansion and contraction of the chest, which is called respiratory movement, including inhalation and exhalation. Breathing movement realizes the ventilation of the lungs, that is, the air in the lungs exchanges with the outside air. Inhale when breathing calmly: the intercostal muscles and diaphragm contract → the ribs move upward and outward, and the diaphragm top descends → the thorax expands → the lung expands → the air pressure in the lung is lower than the outside air pressure → the outside air enters the lung; Exhale: external intercostal muscle and diaphragm relax → ribs descend, diaphragm top rises → chest volume decreases → lung retraction → intrapulmonary pressure > external atmospheric pressure → intrapulmonary gas discharge. So option a fits the question.

Test center: the knowledge point examined in this question is the principle of respiratory movement.