**Core Concept**
The primary goal in managing a patient with multiple injuries is to prioritize their care and ensure that life-threatening conditions are addressed promptly. This involves a systematic approach to assess the patient's airway, breathing, and circulation (ABCs) to prevent further deterioration and optimize their chances of survival.

**Why the Correct Answer is Right**
The correct answer is **A. Establish Airway**: This is the first step in the ABC approach, as a patent airway is essential for maintaining adequate oxygenation and ventilation. The airway is the primary route for oxygen and carbon dioxide exchange, and its patency is crucial for preventing hypoxia and hypercarbia. Establishing an airway also facilitates the administration of oxygen and other medications, which is critical in the initial management of a patient with multiple injuries.

**Why Each Wrong Option is Incorrect**
* **Option B:** While assessing breathing is an essential part of the ABC approach, it is not the first step. Breathing can be assessed and managed once the airway is established.
* **Option C:** Circulation is an important aspect of patient care, but it is not the first priority in managing a patient with multiple injuries. Establishing an airway and ensuring adequate oxygenation and ventilation are critical before addressing circulatory issues.
* **Option D:** While pain management is an essential aspect of patient care, it is not the first step in managing a patient with multiple injuries. The initial focus is on stabilizing the patient's ABCs and preventing further deterioration.

**Clinical Pearl / High-Yield Fact**
The ABC approach is a fundamental principle in emergency medicine, and it is essential to remember that the order of assessment is airway, breathing, and then circulation. This systematic approach helps ensure that life-threatening conditions are addressed promptly, and it is a critical skill for all healthcare professionals to master.

**Correct Answer: A. Establish Airway**