The nurse would include in a teaching plan about mouth care for a child receiving chemotherapy to:

A. Rigid abdomen: A rigid abdomen is not a common finding in HPS. However, it is more typical in conditions such as intestinal obstruction.

B. Distended neck veins: Distended neck veins are not a typical manifestation of HPS. They may be associated with other cardiovascular or respiratory issues.

C. Red currant jelly stools: Red currant jelly-like stools are not typically seen in HPS. This description is often used to describe the appearance of stools in intussusception, which is a different gastrointestinal condition.

D. Projectile vomiting.

Hypertrophic pyloric stenosis is a condition in infants where the muscle at the outlet of the stomach (pylorus) becomes thickened and obstructs the passage of food from the stomach into the small intestine. Projectile vomiting is a characteristic symptom of HPS. The vomit is forceful and seems to shoot out of the infant's mouth, typically occurring after feeding.

A.Pyloric stenosis is a condition where there's narrowing of the opening between the stomach and the small intestine. It is not related to inadequate motility of the intestine.

B.Enterocolitis refers to inflammation of the small intestine and colon. While this can cause obstruction in some cases, it's not the primary cause of inadequate motility as seen in the question.

C.Encopresis is the voluntary or involuntary passage of feces outside the toilet in children who should be toilet trained. It is not a cause of mechanical intestinal obstruction.

D. Hirschsprung's disease is a congenital disorder where there is inadequate motility in part of the intestine, leading to mechanical obstruction. It usually affects the colon and is due to the absence of ganglion cells in the affected segment of the bowel.

So, Hirschsprung's disease is the specific condition that leads to inadequate motility and mechanical obstruction of part of the intestine in infants.