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Question:

Which of the following best explains how inhalation occurs in the human respiratory system?

A the diaphragm contracts and lowers, making the air pressure in the lungs decrease.
Explaination

During exhalation, the air pressure in the lungs must increase greater than atmospheric pressure, to force the air out of the lungs. To increase pleural pressure, the diaphragm relaxes and lifts. The reverse occurs during inhalation, whereby the diaphragm contracts and lowers itself, making the volume increase in the lungs, and pressure decrease in the lungs, therefore forcing air into the lungs.[Human Body Science]