**Core Concept**
The placement of a double lumen tube (DLT) in lung surgery is crucial for separate ventilation of each lung and to prevent aspiration. The correct positioning of the DLT is confirmed by verifying the correct placement of the bronchial cuff in the main bronchus and the tracheal cuff at the level of the carina.

**Why the Correct Answer is Right**
The correct placement of the DLT is confirmed by **fiberoptic bronchoscopy (FOB)**, which allows the anesthesiologist to visualize the tracheal and bronchial cuffs in relation to the carina and the main bronchi. FOB also helps to confirm that the bronchial cuff is not too close to the carina, which can lead to obstruction of the contralateral main bronchus. This is especially important in patients undergoing lung surgery, where accurate ventilation of each lung is critical.

**Why Each Wrong Option is Incorrect**
**Option A:** **Chest X-ray** is not sufficient to confirm the correct placement of the DLT, as it may not accurately depict the position of the bronchial cuff in relation to the carina.
**Option B:** **Capnography** can confirm the correct placement of the endotracheal tube, but it cannot confirm the correct placement of the bronchial cuff in the main bronchus.
**Option D:** **Clinical assessment** alone is not sufficient to confirm the correct placement of the DLT, as it may not accurately reflect the position of the bronchial cuff in relation to the carina.

**Clinical Pearl / High-Yield Fact**
In patients undergoing lung surgery, the use of a DLT requires careful coordination with the surgical team to ensure that the bronchial cuff is not obstructing the contralateral main bronchus, which can lead to inadequate ventilation of the lung.

**Correct Answer:** C.