**Core Concept**
The question pertains to confirming the correct placement of a double-lumen endotracheal tube (DLT) during lung surgery, which is crucial for selective lung ventilation. A DLT has two separate lumens, one for each lung, allowing for independent ventilation and protection of the non-operative lung.

**Why the Correct Answer is Right**
The correct placement of a DLT is confirmed by checking the position of the endobronchial cuff. The endobronchial cuff should be situated in the right main bronchus to ensure that the left lung is isolated and not ventilated. This is achieved by feeling for the resistance when the tube is advanced further into the right main bronchus. The correct placement can also be confirmed by using a bronchoscope, which can visualize the position of the tube inside the airways.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, so we cannot assess its correctness.
* **Option B:** This option is also not provided, so we cannot assess its correctness.
* **Option C:** This option is not provided, so we cannot assess its correctness.
* **Option D:** This option is also not provided, so we cannot assess its correctness.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the correct placement of a DLT can be confirmed by the resistance felt when advancing the tube into the right main bronchus and by visualizing the tube's position using a bronchoscope. This is crucial to prevent complications such as lung injury or inadequate ventilation.

**Correct Answer: D. Chest X-ray.**