Answer: B. Endoscopy.

Because the patient is symptomatic, endoscopy is indicated.

A CT scan of the chest is useful for organic and inorganic materials.

A basic chest radiograph cannot reliably exclude a foreign body.

Barium swallow is difficult in pediatric patients, particularly this child, who is refusing oral fluids.

Water-soluble media risk pneumonitis if aspirated. Non–water-soluble materials risk increased inflammation if leakage occurs into the mediastinum. Barium may also obscure subsequent endoscopic visualization.