**Core Concept**
Neuroblastoma is the most common extracranial solid tumor in infants, arising from the sympathetic nervous system. It typically presents in the adrenal glands, but can also occur in the neck, chest, or pelvis.

**Why the Correct Answer is Right**
Neuroblastoma originates from the neural crest cells that migrate to various parts of the body during fetal development. The tumor can produce excess catecholamines, leading to symptoms such as hypertension, tachycardia, and flushing. The diagnosis is often confirmed by imaging studies, such as ultrasound or CT scans, and further evaluated by tumor markers like urinary vanillylmandelic acid (VMA).

**Why Each Wrong Option is Incorrect**
* **Option A:** Although lymphoma is a common childhood cancer, it is not the most common tumor in infants.
* **Option B:** Rhabdomyosarcoma is a type of soft tissue sarcoma, but it is not the most common tumor in infants.
* **Option C:** Wilms tumor is a common kidney cancer in children, but it is more common in children aged 2-4 years, not typically in infants.

**Clinical Pearl / High-Yield Fact**
Neuroblastoma often presents with a triad of symptoms: abdominal mass, abdominal pain, and weight loss. A high level of urinary VMA can support the diagnosis of neuroblastoma.

**Correct Answer: C. Neuroblastoma.**