Pancreatic juice .

Correct Answer: D

Rationale: The correct answer is D because pancreatic juice buffers chyme, the acidic mixture of partially digested food from the stomach. This buffering action helps maintain the pH level for optimal enzymatic activity in the small intestine. Choice A is incorrect because pancreatic juice does not deactivate bile; bile aids in the digestion and absorption of fats. Choice C is incorrect as pancreatic islet cells secrete hormones like insulin and glucagon, not pancreatic juice. Choice B is incomplete and irrelevant, providing no information related to pancreatic juice function.

Correct Answer: B

Rationale: The correct answer is B: haustra. The large intestine has haustra, which are pouches formed by muscle contractions that help in moving feces along the colon. Villi (choice A) and microvilli (choice C) are features of the small intestine, aiding in nutrient absorption. Lacteals (choice D) are lymphatic vessels in the small intestine. Therefore, the presence of haustra is a distinct feature of the large intestine, making it the correct choice in this context.

Correct Answer: B

Rationale: The correct answer is B. The small intestine is where the majority of digestion and absorption occur due to its large surface area for nutrient absorption. This is facilitated by villi and microvilli. Choice A is incorrect as the small intestine is lined with villi and microvilli, not smooth muscle. Choice C is incorrect because bile is produced in the liver and stored in the gallbladder. Choice D is incorrect as carbohydrate digestion primarily occurs in the mouth and small intestine.

Correct Answer: B

Rationale: The correct answer is B: amylase. Amylase is responsible for breaking down carbohydrates into smaller sugar molecules in the digestive system. It is produced in the saliva and pancreas. Lipase (A) digests fats, pepsin (C) digests proteins, and trypsin (D) also digests proteins, not carbohydrates. Therefore, amylase is the correct enzyme for carbohydrate digestion.

Correct Answer: D

Rationale: Saliva does not contain platelets because platelets are components of blood responsible for blood clotting, not found in saliva. Saliva does contain ABO blood group antigens, lysozymes for antibacterial activity, and immunoglobulins for immune function. Platelets are not a normal component of saliva, making option D the correct answer.