Correct Answer: C

Rationale: The correct answer is Vitamin B3, also known as Niacin. Niacin is essential for energy metabolism and can help improve cholesterol levels. Vitamin B1 is Thiamine, Vitamin B2 is Riboflavin, and Vitamin B12 is Cobalamin. These vitamins have different functions in the body and are not synonymous with Niacin.

Correct Answer: B

Rationale: Patients with congestive heart failure need to restrict their intake of sodium. This restriction is crucial to prevent fluid retention, which can exacerbate the condition. While fiber is generally beneficial for heart health, sodium restriction is more critical in this scenario. Cholesterol and saturated fat intake should also be monitored, but sodium restriction takes precedence due to its direct impact on fluid balance.

Correct Answer: B

Rationale: Reduced stomach acidity impairs the absorption of iron, as an acidic environment is necessary for optimal iron absorption in the stomach. Choices A, C, and D are incorrect as medications that reduce stomach acidity typically do not significantly affect the absorption of calcium, vitamin D, or vitamin C.

Correct Answer: B

Rationale: The correct answer is B, contracting the uterus. Breastfeeding helps contract the uterus after childbirth, reducing postpartum bleeding and helping the uterus return to its pre-pregnancy size more quickly. Choices A, C, and D are incorrect because conserving calcium stores, protecting against future hypertension, and speeding the resumption of ovulation are not direct benefits of breastfeeding to the mother.

Correct Answer: C

Rationale: The correct answer is C, leptin. Leptin is a hormone produced by fat cells that helps regulate energy balance by suppressing hunger, thus aiding in the regulation of body fat. Glucagon (choice A) is a hormone that raises blood glucose levels, ghrelin (choice B) stimulates appetite, and insulin (choice D) regulates blood sugar levels and promotes glucose uptake.