Taste buds occur most commonly:

Correct Answer: B

Rationale: The correct answer is B because taste buds are commonly found on the sides of fungiform and circumvallate papillae. Fungiform papillae are mushroom-shaped and scattered on the entire tongue, while circumvallate papillae are large and located at the back of the tongue in a V shape. Taste buds house taste receptor cells responsible for detecting different tastes. Choices A, C, and D are incorrect because taste buds are not mainly located on the tips of filiform papillae, in the crypts of lingual tonsils, or only on the tip of the tongue, respectively.

Correct Answer: D

Rationale: The correct answer is D: anal canal. The anal canal is not characterized by simple columnar epithelium on the mucosal surface. Instead, it is lined by stratified squamous epithelium, which is more suited to withstand the mechanical stress associated with the passage of feces. The stomach (A), small intestine (B), and appendix (C) all have simple columnar epithelium to facilitate absorption and secretion. Therefore, the anal canal is the only region among the choices that does not have simple columnar epithelium, making it the correct answer.

Correct Answer: B

Rationale: The stomach has thick mucosa with diverse glandular cells (parietal, chief, etc.).

Correct Answer: D

Rationale: All listed features distinguish the pancreas (endocrine islets, centroacinar cells) from the parotid (adipocytes).

Correct Answer: B

Rationale: Villi are approximately 0.5-1 mm long, enhancing absorption.