**Core Concept**
In cases of suspected abdominal trauma, the primary goal is to detect any potential internal injuries, such as bleeding or organ damage, which may not always be immediately apparent. The choice of investigation depends on the patient's hemodynamic status, with stable patients typically undergoing imaging studies to evaluate for occult injuries.

**Why the Correct Answer is Right**
In a hemodynamically stable patient with severe abdominal trauma, the best investigation is a non-contrast computed tomography (CT) scan of the abdomen and pelvis. This imaging modality is highly sensitive for detecting free fluid in the abdominal cavity, which may indicate internal bleeding or organ injury. The non-contrast aspect is crucial, as it helps to identify free blood without the need for intravenous contrast, which may obscure small amounts of blood.

**Why Each Wrong Option is Incorrect**
**Option A:** Focused Assessment with Sonography for Trauma (FAST) is a bedside ultrasound examination that can be useful in unstable patients or those with obvious signs of bleeding. However, it is less sensitive than CT for detecting free fluid and may not be as reliable in stable patients.

**Option B:** X-ray of the abdomen is not a suitable investigation for abdominal trauma, as it may not detect occult injuries and can be affected by the presence of bowel gas or other artifacts.

**Option C:** Magnetic Resonance Imaging (MRI) is not typically used in the acute setting of abdominal trauma due to its longer scanning time, limited availability, and potential for artifacts.

**Option D:** Angiography may be used in specific cases of suspected vascular injury, but it is not the initial investigation of choice for abdominal trauma.

**Clinical Pearl / High-Yield Fact**
In stable patients with abdominal trauma, it's essential to perform a thorough physical examination, including a detailed abdominal exam, and to consider the use of a trauma protocol to ensure that all necessary investigations are performed in a timely manner.

**Correct Answer: C. CT scan of the abdomen and pelvis.