Correct Answer: B

Rationale: The correct answer is B: Projectile vomiting. Pyloric stenosis in infants typically presents with projectile vomiting, which is forceful and projective in nature. This occurs due to the obstruction at the pylorus, leading to the stomach being unable to empty properly. Choices A, C, and D are incorrect. Bilious vomiting is more commonly associated with intestinal obstruction, blood in stools can occur in conditions such as necrotizing enterocolitis or allergic colitis, and failure to thrive is a nonspecific finding that can be seen in various pediatric conditions.

Correct Answer: C

Rationale: Allowing the child to assume a position of comfort is appropriate as it helps alleviate discomfort without the risk of complications. Placing the child in the Trendelenburg position could increase intra-abdominal pressure and worsen the condition. Applying moist heat may lead to vasodilation and potential perforation in case of appendicitis. Administering a saline enema can be harmful if the appendix is inflamed or perforated.

Correct Answer: A

Rationale: Polyarthritis is indeed frequently the initial sign of acute rheumatic fever in children. It presents as joint pain, swelling, and redness. Carditis (inflammation of the heart), Erythema marginatum (a skin rash), and Sydenham chorea (involuntary muscle movements) are typically seen in the later stages of acute rheumatic fever and not as the initial sign.

Correct Answer: A

Rationale: The Ortolani sign is a specific maneuver used during physical examination to detect hip instability or dislocation in infants. A positive Ortolani sign, where the hip is felt to slip back into the socket, is indicative of developmental dysplasia of the hip, a condition that can lead to long-term disability if not treated early. Romberg sign is used to assess sensory ataxia, Trendelenburg sign indicates weakness of the hip abductor muscles, and Gower's sign is seen in children with proximal muscle weakness climbing up their own body from a supine position due to conditions like muscular dystrophy.

Correct Answer: A

Rationale: Respiratory infections are the leading cause of morbidity and mortality in children with cystic fibrosis. Cystic fibrosis primarily affects the respiratory system, leading to thick mucus buildup in the lungs, which predisposes these children to recurrent respiratory infections. Malnutrition and diabetes are common comorbidities in cystic fibrosis but are not the leading causes of morbidity and mortality in affected children. Liver disease can occur in cystic fibrosis but is less common than respiratory complications.