Correct Answer: D

Rationale: The most crucial factor in the process of toilet training is the parents' willingness to consistently engage and work with their child. While parents' attitude and the child's desire to remain dry can influence the process, the key to successful toilet training lies in the parents' commitment and effort. The child's ability to sit still on the toilet is important but not as critical as the parents' active involvement and support in guiding and encouraging the child through the training process.

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: The correct answer is D: Severe coughing spells. Pertussis, also known as whooping cough, typically presents with severe coughing spells that can be followed by a characteristic 'whoop' sound. These coughing fits can be intense and prolonged, often causing the child to gasp for air between coughs. Option A, dry hacking cough, is a common symptom of other respiratory conditions like bronchitis. Option B, inspiratory stridor, is more commonly associated with conditions like croup. Option C, nasal congestion, is not a typical symptom of pertussis.

Correct Answer: A

Rationale: The American Academy of Pediatrics recommends the intramuscular polio vaccine over the oral vaccine due to its superior safety profile. Intramuscular administration ensures better immunogenicity and protection against poliovirus. Choice B is incorrect as the intramuscular vaccine is preferred for safety reasons. Choice C is incorrect because the recommendation is based on safety, not cost. Choice D is incorrect as the CDC recommendation is not solely based on immunocompromised status but rather on the overall safety and efficacy of the vaccine.

Correct Answer: C

Rationale: Scheduling the visit at a time that is convenient for the family is the most appropriate choice. This ensures that the family is receptive and available, making the visit more productive. Choice A is incorrect because the presence of the husband may be important for support and decision-making. Choice B focuses solely on the mother and the infant's feeding time, which may not align with the family's overall availability. Choice D is incorrect as it emphasizes the nurse's convenience rather than the family's, which may not lead to an effective visit.