In neonates, apnea of prematurity is due to:

Correct Answer: B

Rationale: Apnea of prematurity is caused by an immature central respiratory drive in preterm infants. It leads to intermittent pauses in breathing and can be managed with caffeine therapy and respiratory support if needed.

Correct Answer: B

Rationale: Medullary relapse, or recurrence of leukemia in the bone marrow, is the most common form of relapse in acute leukemia, requiring additional chemotherapy.

Correct Answer: D

Rationale: Attention-deficit/hyperactivity disorder (ADHD) is frequently comorbid with autism, affecting attention and impulse control.

Correct Answer: C

Rationale: Croup is more common in males, affecting young children with a characteristic barking cough and stridor. Parainfluenza virus is the leading cause, with peak incidence around 6 months to 3 years.

Correct Answer: C

Rationale: Dilute artificial formula can lead to hyponatremia and total body sodium depletion, whereas SIADH causes water retention rather than true sodium loss.