Correct Answer: A

Rationale: Phosphorus is the correct answer. It is a key component of cell membranes, being part of the phospholipid bilayer that provides structure and controls the movement of substances in and out of cells. Magnesium, iron, and iodine do not serve as principal components of cell membranes. Magnesium is involved in various enzymatic reactions, iron is essential for oxygen transport, and iodine plays a role in thyroid hormone synthesis.

Correct Answer: B

Rationale: The statement that the major function of vitamin E is promoting vision is incorrect. Vitamin E primarily acts as an antioxidant, protecting cells from oxidative damage. Its role is not primarily related to vision, which is a major function of vitamin A. On the other hand, the other options are true. Vitamin K deficiency does indeed lead to increased clotting time, vitamin D functions as a hormone, and carrots, sweet potatoes, and butternut squash are rich sources of beta-carotene.

Correct Answer: C

Rationale: The placenta plays a crucial role in producing hormones that are necessary for maintaining pregnancy, supporting fetal development, and preparing the mother's body for childbirth. Choices A, B, and D are incorrect because the placenta's primary function is not to surround and cushion the fetus, combine blood stores for nutrient exchange, or absorb vitamins and minerals. While the placenta does facilitate the exchange of nutrients and oxygen between the mother and fetus, its hormone production is the most critical function during pregnancy.

Correct Answer: A

Rationale: Phosphorus is the correct answer. It is a key component of cell membranes, being part of the phospholipid bilayer that provides structure and controls the movement of substances in and out of cells. Magnesium, iron, and iodine do not serve as principal components of cell membranes. Magnesium is involved in various enzymatic reactions, iron is essential for oxygen transport, and iodine plays a role in thyroid hormone synthesis.

Correct Answer: A

Rationale: The correct answer is A. Folate plays a crucial role in DNA synthesis and cell division, which are essential processes for cell multiplication. This makes folate particularly important during periods of rapid growth, such as pregnancy. Therefore, the statement is true. Choice B is incorrect because it fails to acknowledge the significance of folate in cell multiplication and rapid growth, especially during pregnancy.