Correct Answer: C

Rationale: The correct answer is C. Mast cells are responsible for releasing histamine and other chemicals during an allergic response. Choice A is incorrect because hives and wheezing are symptoms of an allergic reaction, not the causes. Choice B is incorrect as B-cells are not directly involved in allergic reactions. Choice D is incorrect as keratin and collagen are not typically involved in allergic reactions, and histamine is released by mast cells.

Correct Answer: B

Rationale: The correct answer is B. To measure the volume of a cube, you need to use a mathematical formula that takes into account the dimensions of the cube, specifically the length of its sides. Using a measuring wheel alone or a triple beam balance is not suitable for determining the volume of a cube. A graduated cylinder is used to measure the volume of liquids, not geometric solids like cubes.

Correct Answer: B

Rationale: The correct answer is the Hypothalamus (choice B). The hypothalamus plays a crucial role in maintaining homeostasis by regulating various bodily functions such as hunger, thirst, body temperature, and sleep cycles. While the brainstem (choice A) is involved in basic life functions like breathing and heart rate, it is not primarily responsible for maintaining homeostasis. The medulla oblongata (choice C) is part of the brainstem and controls vital autonomic functions like breathing and heart rate, but it is not the main regulator of homeostasis. The cerebrum (choice D) is responsible for higher brain functions such as thinking, memory, and voluntary movement, but it is not directly involved in maintaining overall bodily balance or homeostasis.

Correct Answer: B

Rationale: Vitamin D is the correct answer. When the skin is exposed to sunlight, it triggers a process where a form of cholesterol in the skin is converted into vitamin D. This vitamin plays a crucial role in aiding calcium absorption in the gut, which is essential for maintaining strong and healthy bones. Vitamin A (Choice A) is important for vision and immune function but is not produced by sunlight exposure. Vitamin K (Choice C) is known for its role in blood clotting and bone metabolism, but it is not produced by sunlight. Vitamin E (Choice D) is an antioxidant that protects cells from damage but is not synthesized in the skin through sunlight exposure.

Correct Answer: B

Rationale: White blood cells play a crucial role in the immune system by fighting infection and protecting the body from foreign invaders. Choice A, 'To transport oxygen,' is incorrect because red blood cells are responsible for transporting oxygen. Choice C, 'To carry oxygen,' is also inaccurate for the same reason. Choice D, 'To produce antibodies,' while related to the immune system, is not the primary function of white blood cells, as their main role is to directly combat infections.