Neonatal liver system processes food, extracts nutrients, and eliminates the residue.

A. Esophageal glands secrete mucus to lubricate the esophagus, but they do not cause acid reflux.

B. Pharyngeal constrictors are muscles that help in the swallowing process, not in preventing acid reflux.

C. The lower esophageal sphincter (LES) is a ring of muscle that controls the passage of food from the esophagus to the stomach. If the LES is weakened or relaxes inappropriately, stomach acid can flow back into the esophagus, causing acid reflux or "heartburn."

D. The upper esophageal sphincter controls the passage of food from the pharynx into the esophagus, but it is not involved in preventing acid reflux.

A. It increases both Na+ and K+ secretion: Aldosterone increases sodium (Na+) reabsorption and potassium (K+) secretion, but it does not increase the secretion of both ions.

B. It causes the urine to be more diluted. Aldosterone causes the urine to be more concentrated by increasing sodium reabsorption and potassium secretion.

C. It reduces Na+ reabsorption and K+ secretion. Aldosterone actually increases sodium reabsorption and potassium secretion, not reduces them.

D. It increases Na+ reabsorption and K+ secretion. Aldosterone promotes sodium reabsorption in the kidneys and increases potassium secretion, leading to more concentrated urine.