The main muscle responsible for pulmonary ventilation is?.

The correct answer is Choice A.

Choice A rationale:

The pleural fluid functions by lubricating the space between the pleura, allowing the pleura to glide smoothly during inhalation and exhalation. This cushions delicate lung tissues against friction from the ribs and the chest wall itself.

Choice B rationale:

The fluid in the pleural cavity does not warm and moisten lung tissue. This is not one of its primary functions.

Choice C rationale:

The fluid in the pleural cavity does not prevent bacteria from entering lung tissue. This is not one of its primary functions.

Choice D rationale:

The fluid in the pleural cavity does not assist in the diffusion of oxygen across the respiratory membrane. This is not one of its primary functions.

Choice A rationale:

While the nasopharynx does play a role in warming and moistening inspired air, this is not its primary function.

Choice B rationale:

The nasopharynx does not primarily filter dust. This function is mainly performed by the nasal cavity and the hairs within the nostrils.

Choice C rationale:

The nasopharynx provides openings for the right and left Eustachian tubes. These tubes connect the middle ear to the nasopharynx and help equalize air pressure on either side of the eardrum.

Choice D rationale:

The nasopharynx does not contain olfactory receptors responsible for the sense of smell. These receptors are located in the nasal cavity.