Correct Answer: B

Rationale: The correct answer is Iron. Iron is essential for the formation of hemoglobin, the protein in red blood cells that binds and transports oxygen throughout the body. Calcium (Choice A), Potassium (Choice C), and Sodium (Choice D) are not directly involved in the formation of hemoglobin and its oxygen-carrying function.

Correct Answer: B

Rationale: The correct answer is Iron. Iron is essential for the formation of hemoglobin, the protein in red blood cells that binds and transports oxygen throughout the body. Calcium (Choice A), Potassium (Choice C), and Sodium (Choice D) are not directly involved in the formation of hemoglobin and its oxygen-carrying function.

Correct Answer: C

Rationale: The correct answer is C. While many macromolecules contain carbon, hydrogen, and phosphorus, not all of them do. For example, lipids, a type of macromolecule, may not contain phosphorus. Choice A and B describe structural features that macromolecules can exhibit, whether as single chains or branched forms. Choice D is incorrect as not all macromolecules are used by the body, such as synthetic polymers or certain non-digestible fibers.

Correct Answer: D

Rationale: The correct answer is D: To regulate blood glucose. The adrenal glands play a crucial role in regulating blood glucose levels and the body's response to stress. Choice A, 'To regulate metabolism,' is incorrect as the primary role of the adrenal glands is not directly related to metabolism regulation. Choice B, 'To produce bile,' is incorrect because bile is produced by the liver, not the adrenal glands. Choice C, 'To produce red blood cells,' is also incorrect as the production of red blood cells primarily occurs in the bone marrow, not the adrenal glands.

Correct Answer: D

Rationale: The correct answer is D, 'All of the above.' The large intestine performs various functions, including the absorption of water, production of vitamin K, and production of some B vitamins. Water absorption is a crucial function of the large intestine, helping to concentrate waste material into feces. Additionally, the large intestine hosts beneficial bacteria that produce vitamin K and some B vitamins, which are absorbed into the body. Choices A, B, and C individually represent specific functions of the large intestine, while choice D correctly encompasses all these functions, making it the most comprehensive and accurate answer.