Correct Answer: A

Rationale: The correct answer is A: provide energy. Nutrients play a crucial role in providing energy for the body's various functions. While they do help in regulating metabolic processes and in building and repairing tissue, the primary function related to energy production. Choices B, C, and D are incorrect as nutrients are not primarily responsible for controlling cellular wastes, hormone levels, or absorption.

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.

Correct Answer: A

Rationale: One slice of bread is a standard serving from the Grains group in MyPlate. This choice aligns with the recommended portion size for grains. Choices B, C, and D are excessive portions that do not represent a single serving according to MyPlate guidelines. 2 cups of rice, 3 cups of spaghetti, and 4 oz of ready-to-eat cereal exceed the standard serving size for grains and would provide more than one serving from this food group.

Correct Answer: A

Rationale: The correct answer is iron. Iron is essential for enzyme function and energy production within the mitochondria. While cobalt is important for certain enzymes, it is not the primary mineral involved in this specific function. Hemoglobin is a protein in red blood cells that carries oxygen, not a mineral involved in enzyme actions. Vitamin B12 is crucial for nerve function and DNA synthesis but is not directly related to controlling enzyme actions in mitochondria.

Correct Answer: B

Rationale: The correct answer is B: 120. Carbohydrates provide 4 kcal per gram, so 30 grams of carbohydrates will provide 120 kcal. This is calculated by multiplying the grams of carbohydrate (30) by the kcal per gram (4). Choices A, C, and D are incorrect because they do not reflect the correct calculation based on the energy content of carbohydrates.