Correct Answer: B

Rationale: Vitamin A is the correct answer. It is essential for maintaining healthy skin and vision, especially in low-light conditions. Vitamin A helps in the production of retinal pigments necessary for vision in dim light and supports skin health by promoting cell turnover and repair. Choice A, Vitamin C, is important for the immune system and collagen production but is not specifically known for maintaining skin and vision health. Choice C, Vitamin D, is crucial for bone health and immune function but is not directly related to skin and vision health. Choice D, Vitamin K, is necessary for blood clotting and bone health but does not play a significant role in maintaining healthy skin and vision.

Correct Answer: B

Rationale: Vitamin A is the correct answer. It is essential for maintaining healthy skin and vision, especially in low-light conditions. Vitamin A helps in the production of retinal pigments necessary for vision in dim light and supports skin health by promoting cell turnover and repair. Choice A, Vitamin C, is important for the immune system and collagen production but is not specifically known for maintaining skin and vision health. Choice C, Vitamin D, is crucial for bone health and immune function but is not directly related to skin and vision health. Choice D, Vitamin K, is necessary for blood clotting and bone health but does not play a significant role in maintaining healthy skin and vision.

Correct Answer: B

Rationale: The correct answer is B: 'To break down food.' The stomach's primary function in digestion is to break down food mechanically and chemically. It accomplishes this by mixing food with gastric acid and digestive enzymes, resulting in the formation of chyme, a semi-liquid mixture that moves on to further digestion in the small intestine. Choice A is incorrect because the absorption of nutrients occurs mainly in the small intestine, not in the stomach. Choice C is incorrect because while the stomach does secrete digestive enzymes like pepsin, its primary role is not just limited to enzyme secretion. Choice D is incorrect because the storage of glucose primarily occurs in the liver and muscles, not in the stomach.

Correct Answer: B

Rationale: The primary function of platelets, or thrombocytes, is to clot blood. Platelets play a crucial role in hemostasis by forming clots to prevent excessive bleeding when injuries occur. They are not directly involved in fighting infections, carrying oxygen, or transporting nutrients. Therefore, the correct answer is B.

Correct Answer: B

Rationale: The medulla oblongata, located in the brainstem, plays a crucial role in controlling vital functions such as breathing, heart rate, and blood pressure. It serves as the control center for automatic functions necessary for survival, making it the correct choice in this scenario. The cerebrum is responsible for higher brain functions like thinking and voluntary movements, so it does not control basic physiological functions like breathing and heart rate. The cerebellum is mainly involved in coordination and balance, while the hypothalamus regulates body temperature, hunger, and thirst, but not specifically breathing and heart rate.