All the following can cause metabolic acidosis with high anion gap Except:

Correct Answer: C

Rationale: Renal tubular acidosis typically causes normal anion gap metabolic acidosis rather than an increased anion gap.

Correct Answer: A

Rationale: The correct answer is A because the bones surrounding the posterior fontanel typically fuse and close by age 6 to 8 weeks. This closure is a normal part of infant development.

Correct Answer: B

Rationale: The correct answer is B. The best age to introduce solid foods into an infant's diet is typically between 4 to 6 months. At this age, the infant's digestive system has matured enough to handle more complex nutrients, and they have likely lost the extrusion reflex, making swallowing easier. It is an important transition period for introducing new foods.

Correct Answer: B

Rationale: Tetralogy of Fallot consists of four defects: pulmonary stenosis, right ventricular hypertrophy, overriding aorta, and VSD. The boot-shaped heart on X-ray is a classic finding. Cyanotic spells improve with squatting or knee-chest positioning.

Correct Answer: A

Rationale: Skin thickening due to fibrosis is a hallmark feature of scleroderma.