Final answer:
Fecal impaction, which is the most serious form of constipation, occurs when feces become very hard and dry and cannot be expelled naturally, often requiring medical intervention. D. the most serious form of constipation.
Step-by-step explanation:
Fecal impaction is D. the most serious form of constipation, where feces become so hard and dry that they cannot be expelled from the body naturally. This condition occurs when defecation is delayed for an extended time, leading to additional water absorption and very firm feces.
If wastes move too quickly through the intestines, not enough water is reabsorbed, which can result in diarrhea. Conversely, when feces move too slowly through the colon, more water gets absorbed, increasing the risk of constipation. Fecal impaction may require medical intervention, such as manual removal or medication.