Correct Answer: B

Rationale: A low-phenylalanine diet is crucial for managing PKU to prevent neurological damage and maintain normal development. Phenylalanine is an amino acid found in protein-containing foods, and individuals with PKU have difficulty metabolizing it. Consuming foods low in phenylalanine helps prevent the buildup of toxic byproducts in the body. Choices A, C, and D are incorrect. A high-fiber diet, increased dairy intake, and high-sodium diet are not specific dietary considerations for PKU management. In fact, dairy products are a source of protein and phenylalanine, which should be limited in PKU.

Correct Answer: C

Rationale: An essential nutrient is a substance that cannot be made in sufficient quantities by the body itself, so it must be obtained from the diet. Choice A is incorrect because essential nutrients are required in specific amounts, not necessarily large quantities. Choice B is incorrect as essential nutrients cannot be synthesized by the body at all. Choice D is incorrect because although essential nutrients may be used in the synthesis of other compounds, that is not the defining characteristic of an essential nutrient.

Correct Answer: D

Rationale: The correct answer is 'negative association.' A negative association occurs when a person develops a dislike for a food due to a past negative experience, such as getting sick after eating it. In this case, the child's dislike of noodle soup is specifically linked to the negative experience of consuming it while sick with the flu. Choices A, B, and C are incorrect because the situation described does not relate to habit formation, social interactions, or emotional turmoil, but rather to a learned aversion based on a specific negative event.

Correct Answer: D

Rationale: The correct answer is D. Carbohydrates are the body's primary source of energy, fueling daily activities and bodily functions. Choice A is incorrect because insulation and organ support are primarily provided by adipose tissue and structural proteins, not carbohydrates. Choice B is incorrect because the regulation of body temperature is mainly controlled by processes like sweating and shivering, not carbohydrates. Choice C is incorrect because structural components like proteins are responsible for building tissues and organs, not carbohydrates.

Correct Answer: C

Rationale: Dry skin and constipation are typical signs of hypothyroidism in children. Hypothyroidism results from an underactive thyroid gland, leading to symptoms such as dry skin and constipation. Weight loss (Choice A) is more commonly associated with hyperthyroidism, where the thyroid gland is overactive. Increased heart rate (Choice B) and elevated blood pressure (Choice D) are also more characteristic of hyperthyroidism rather than hypothyroidism. Therefore, the correct answer is dry skin and constipation (Choice C) when identifying signs of hypothyroidism in children.