**Core Concept**
The placement of a double-lumen tube (DLT) is crucial for one-lung ventilation in thoracic surgery, ensuring proper ventilation and anesthetic management of the patient. A DLT is a specialized endotracheal tube with two separate lumens that allow for selective ventilation of one lung while the other is deflated.

**Why the Correct Answer is Right**
The correct answer is confirmed by endoscopy, which allows visualization of the DLT's position within the airway, ensuring that the bronchial cuff is correctly placed in the left mainstem bronchus and the tracheal cuff is positioned above the carina. This is essential to prevent complications such as bronchial obstruction, pneumothorax, or tracheal injury. Endoscopy provides a clear view of the DLT's position and helps to confirm its correct placement before initiating one-lung ventilation.

**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is not sufficient for confirming DLT placement, as it may not accurately depict the position of the bronchial cuff and can be misleading due to overlapping structures.

**Option B:** Clinical assessment alone is not reliable for confirming DLT placement, as it may not detect subtle misplacements or complications.

**Option C:** Auscultation is not a reliable method for confirming DLT placement, as it may not accurately detect the presence of breath sounds in the non-ventilated lung.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that endoscopy should be performed before initiating one-lung ventilation to confirm DLT placement and prevent complications.

**Correct Answer:** C. Auscultation is not a reliable method for confirming DLT placement, as it may not accurately detect the presence of breath sounds in the non-ventilated lung.