Final answer:
B) Mucus-secreting cells
The mucosa in the mouth, stomach, and small intestine primarily contains mucus-secreting cells that protect the organ lining and absorptive cells in the small intestine that aid in nutrient absorption.
Step-by-step explanation:
In the mouth, stomach, and small intestine, the mucosa contains B) Mucus-secreting cells. These cells are crucial for protecting the lining of these organs by secreting mucus. In the stomach, mucus serves as a protective barrier against the acidic environment necessary for digestion. Absorptive cells are also present in the small intestine's mucosa. These are simple columnar epithelial cells called enterocytes, which are responsible for the majority of nutrient absorption. The mucosa does not produce pancreatic enzymes; these are secreted by the pancreas and delivered to the small intestine. The intestinal glands also secrete intestinal juice that provides a liquid medium facilitating both absorption and enzymatic digestion on the luminal surfaces of the mucosal cells.