The opening between the true vocal cords is called the

A. Muscle contraction of upper airways: Upper airway muscle movement does not create the main pressure change driving inspiration
B. Partial pressure gradients for oxygen and carbon dioxide: Partial pressure gradients drive gas diffusion across membranes, not bulk airflow into lungs
C. Pressure gradient between atmosphere and alveoli: Contraction of the diaphragm/intercostals lowers intrapulmonary pressure relative to atmospheric pressure, causing air to flow in
D. Concentration gradients for oxygen and carbon dioxide: Concentration gradients drive diffusion at the alveolar–capillary level, not the gross movement of air into the lungs

A. Submucosa: submucosa is connective tissue containing blood/lymph vessels and glands, not the epithelial lining.
B. Muscularis: muscularis is smooth muscle (inner circular/outer longitudinal layers) responsible for peristalsis, not epithelial.
C. Mucosa: the mucosa includes the epithelial lining, lamina propria, and may contain folds and mucus-secreting glands (e.g., gastric mucosa).
D. Serosa: serosa is the outermost connective tissue/mesothelial covering of the gut, not the epithelial absorptive/secreting layer.