Correct Answer: C

Rationale: The primary function of carbohydrates as a food source is to supply energy. Carbohydrates are the body's main source of energy, providing fuel for various physiological functions. Choice A is incorrect because carbohydrates do not primarily regulate metabolic processes; that role is mainly attributed to enzymes and hormones. Choice B is incorrect because proteins are primarily responsible for building body tissue. Choice D is incorrect because fiber, not all carbohydrates, provides bulk in the diet.

Correct Answer: A

Rationale: The correct answer is A: Vitamins. Vitamins play a crucial role in tissue building and repair along with protein. Carbohydrates (choice B) are primarily a source of energy and not directly involved in tissue building. Fats (choice C) are important for energy storage and insulation but are not the main contributors to tissue building. Enzymes (choice D) are biological catalysts and do not directly contribute to tissue building and repair.

Correct Answer: C

Rationale: The correct answer is C: phosphorus. Phosphorus, along with calcium, is essential for bone health and maintenance. Potassium (choice A) is important for muscle function, iron (choice B) is crucial for red blood cell production, and fluoride (choice D) helps prevent tooth decay but is not a major mineral needed for bone tissue.

Correct Answer: A

Rationale: Infants are particularly vulnerable to malnutrition due to their high growth rate and specific nutrient requirements. During the first year of life, infants experience rapid growth and development, requiring essential nutrients for proper physical and cognitive development. Teenagers, young adults, and middle-aged adults have more stable nutritional needs compared to infants, making them less vulnerable to malnutrition. Therefore, infants are the most susceptible age group when it comes to malnutrition.

Correct Answer: C

Rationale: The correct answer is C. Understanding serving sizes is crucial because most people have difficulty estimating the amount of food they eat. It helps individuals accurately track their intake, which is essential for maintaining a healthy diet and avoiding overeating. Choice A is incorrect because the question focuses on portion sizes rather than specific nutrients. Choice B is incorrect as it presents an unsupported claim about serving sizes decreasing. Choice D is incorrect as weighing food portions is not always necessary to check serving sizes; understanding standard serving sizes allows for a more practical approach to portion control.