**Core Concept**
The clinical presentation of abdominal distention due to an enlarged liver, uncontrolled hypoglycemia, and ketosis in a child suggests a metabolic disorder affecting glycogen storage and breakdown. This condition is characterized by the inability to store glycogen in the liver, leading to excessive glucose production through gluconeogenesis and lipolysis, resulting in ketosis.

**Why the Correct Answer is Right**
The child's symptoms are consistent with Glycogen Storage Disease Type I (GSD I), also known as von Gierke's disease. This condition is caused by a deficiency of the enzyme glucose-6-phosphatase, which is crucial for the final step of gluconeogenesis and glycogenolysis. As a result, the liver is unable to convert glucose-6-phosphate to glucose, leading to hypoglycemia. The liver also accumulates glycogen, causing hepatomegaly. The body attempts to compensate for the lack of glucose by breaking down fat for energy, resulting in ketosis.

**Why Each Wrong Option is Incorrect**
* **Option B:** McArdle's disease (Glycogen Storage Disease Type V) is a different condition that affects muscle glycogen breakdown, not liver glycogen storage or gluconeogenesis.
* **Option C:** Pompe disease (Glycogen Storage Disease Type II) is caused by a deficiency of the enzyme acid alpha-glucosidase, leading to lysosomal accumulation of glycogen in muscles, not liver enlargement or ketosis.
* **Option D:** Cori's disease (Glycogen Storage Disease Type III) is caused by a deficiency of the debranching enzyme, leading to accumulation of abnormal glycogen in the liver, but not hypoglycemia or ketosis.

**Clinical Pearl / High-Yield Fact**
GSD I is often diagnosed in infancy due to symptoms of hypoglycemia and failure to thrive. However, some cases may present later in childhood or even adulthood, making it essential to consider this diagnosis in any patient with unexplained hepatomegaly and ketosis.

**Correct Answer:** B.