## Core Concept
A pneumonectomy is a surgical procedure involving the removal of a lung, often performed for lung cancer. The surgery requires careful planning and execution to ensure the best possible outcome. The initial steps in the surgery are critical for setting up the procedure.

## Why the Correct Answer is Right
The correct approach when performing a pneumonectomy, especially for cancer of the bronchus, involves careful dissection and identification of key structures. The first step typically involves **ligating and dividing the pulmonary vessels and the mainstem bronchus**. However, before this can be safely done, **exposure and control of the hilum** are essential. This usually starts with **dividing the pulmonary ligament**, which helps in mobilizing the lung and providing better access to the hilar structures. This step is crucial for safely dissecting and ligating the pulmonary vessels and bronchus.

## Why Each Wrong Option is Incorrect
- **Option A:** Without specific details on what "A" entails, it's hard to directly refute, but generally, any step that doesn't prioritize securing the hilum and controlling major vessels and the bronchus would be suboptimal.
- **Option B:** Similarly, without specifics, if "B" does not involve initial control and exposure, it would be incorrect.
- **Option C:** This option is not provided, but presumably, if it were incorrect, it would not align with standard surgical practices for pneumonectomy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that in lung cancer surgery, **preservation of the nerves**, especially the **recurrent laryngeal nerve** and the **phrenic nerve**, is crucial to prevent postoperative complications like vocal cord paralysis and diaphragmatic dysfunction.

## Correct Answer: D. divide the pulmonary ligament.