Final answer:
Expiration is mostly a passive process where no muscles typically contract; the diaphragm and external intercostals relax, leading to lung recoil and air expulsion. correct answer is option D.
Step-by-step explanation:
The student has asked about the process involved in expiration, more specifically about the muscle contractions that lead to exhaling air from the lungs. During quiet breathing, the correct answer to the question is D. No muscles typically contract during expiration as it is primarily a passive process. During expiration, the diaphragm and external intercostal muscles relax rather than contract, allowing the lungs to recoil and air to be expelled. This relaxation leads to an increase in air pressure inside the lungs that drives the air out. However, during a forced exhalation, such as blowing out candles, other muscles like the internal intercostals and abdominal muscles can contract to help force air out more actively.
Expiration is mostly a passive process where no muscles typically contract; the diaphragm and external intercostals relax, leading to lung recoil and air expulsion.