Correct Answer: C

Rationale: The correct answer is C: 9. There are 9 essential amino acids that the body cannot synthesize and must be obtained through the diet. These 9 amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Choices A, B, and D are incorrect as they do not represent the correct number of essential amino acids.

Correct Answer: B

Rationale: The Estimated Average Requirement (EAR) is the correct choice because it is specifically designed to assess the nutrient adequacy of population groups, not individuals. The Recommended Dietary Allowance (RDA) (choice A) is the average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy individuals in a particular life stage and gender group. The Dietary Reference Intake (DRI) (choice C) includes the EAR, RDA, Adequate Intake (AI), and UL, making it a broader set of nutrient reference values. The Tolerable Upper Intake Level (UL) (choice D) is the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population.

Correct Answer: A

Rationale: The correct answer is A: Lysine. Indispensable amino acids are those that the body cannot synthesize and must be obtained from the diet. Lysine, methionine, and tryptophan are all examples of indispensable amino acids. However, the question specifically asked for 3 out of the 9 indispensable amino acids, making 'Lysine' the correct choice. Choices B, C, and D are also indispensable amino acids but are not the focus of the question.

Correct Answer: B

Rationale: Muscle weakness is a common sign of vitamin D deficiency. Vitamin D is essential for calcium absorption and bone health, and its deficiency can lead to muscle weakness. Brittle nails (Choice A) are not typically associated with vitamin D deficiency. Night blindness (Choice C) is related to vitamin A deficiency, not vitamin D deficiency. Hair loss (Choice D) can be linked to various factors, but it is not a common sign of vitamin D deficiency.

Correct Answer: A

Rationale: The correct answer is A: 'breaks down carbs.' Amylase is an enzyme that specifically targets carbohydrates, breaking them down into simpler sugars like maltose. This process aids in the digestion of carbohydrates in the human body. Choices B, C, and D are incorrect because amylase does not break down proteins, lipids, or directly aid fat digestion. Proteins are broken down by proteases, lipids are broken down by lipases, and fat digestion is primarily assisted by bile salts and lipases in the small intestine.