Correct Answer: A

Rationale: The correct answer is to advise the parents to avoid exposure to allergens. Asthma attacks are often triggered by allergens such as dust mites, pollen, pet dander, and mold. By minimizing the child's exposure to these triggers, the likelihood of asthma attacks can be reduced. Encouraging regular exercise is beneficial for overall health but may not directly prevent asthma attacks. Providing a high-protein diet and increasing fluid intake are important for general well-being but do not specifically address asthma prevention.

Correct Answer: A

Rationale: Trisomy 21, also known as Down syndrome, is caused by nondisjunction, which is an error in cell division that leads to the presence of an extra chromosome 21. This additional chromosome alters the normal genetic makeup, resulting in the characteristics associated with Down syndrome. Therefore, the correct answer is nondisjunction (Choice A). Choices B, C, and D are incorrect because Trisomy 21 is not caused by X-linked recessive inheritance, genomic imprinting, or autosomal dominant inheritance. Understanding the specific genetic mechanism involved in Trisomy 21 is crucial for grasping the basis of this chromosomal disorder.

Correct Answer: D

Rationale: A low-phenylalanine diet is necessary for infants with PKU because it helps prevent the accumulation of phenylalanine, which can result in brain damage. Fat-free (Choice A) and protein-enriched (Choice B) diets are not specifically indicated for PKU. While phenylalanine-free (Choice C) may seem logical, complete elimination of phenylalanine is not practical or safe as it is an essential amino acid. Therefore, the correct choice is a low-phenylalanine diet, which restricts phenylalanine intake to a safe level.

Correct Answer: B

Rationale: The correct answer is B. Live vaccines like MMR should not be given to immunosuppressed infants because their weakened immune systems may not handle the vaccine safely. Choice A is incorrect as delaying the MMR vaccine until the infant reaches 2 years of age does not address the issue of immunosuppression. Choice C is incorrect because administering live vaccines to an immunosuppressed individual could lead to serious complications. Choice D is incorrect as immediate action is required to prevent potential harm to the immunosuppressed infant.

Correct Answer: D

Rationale: Macaroni and cheese and Cheerios are appropriate choices for a 30-month-old toddler on a regular diet. These foods are easy to chew, digest, and are generally well-liked by toddlers. Option A, a hamburger with bun and grapes, may be difficult for a toddler to handle due to the size of the hamburger and grapes pose a choking hazard. Option B, chicken fingers and french fries, may be too greasy and processed for a toddler's developing digestive system. Option C, hot dog with bun and potato chips, is also not ideal as hot dogs can be a choking hazard and potato chips are high in salt and may not provide adequate nutrition.