Final answer:
A. Expiration is the only passive process listed, occurring when the diaphragm relaxes and the elasticity of the lungs allows air to flow out without active muscular effort. Inspiration and expiration during exercise can both be active due to the recruitment of additional muscles.
Step-by-step explanation:
Among the options provided, expiration is a passive process. During normal breathing, expiration does not require active muscle contraction. Instead, it occurs mainly due to the elasticity of the lungs when the diaphragm relaxes and the rib cage recoils. This recoil increases the pressure in the lungs above atmospheric pressure, allowing air to flow out in a passive manner.
In contrast, inspiration is an active process involving the contraction of the diaphragm and the external intercostal muscles, which results in the expansion of the thoracic cavity and a reduction of pressure inside the lungs compared to the atmosphere, subsequently leading to the influx of air into the lungs.
During exercise, both inspiration and expiration can become active processes, as additional muscles are recruited to accommodate the increased demand for oxygen and the expulsion of carbon dioxide. This means that both 'inspiration during exercise' and 'expiration during exercise' can involve active muscular effort and are not considered purely passive.