**Core Concept**
In cases of suspected appendicitis with inconclusive ultrasound findings, the next step involves further evaluation to confirm or rule out appendicitis. This requires a diagnostic modality that can provide more detailed imaging of the abdominal cavity, particularly the appendix.

**Why the Correct Answer is Right**
The correct answer involves using computed tomography (CT) scan, which is a highly sensitive and specific imaging modality for diagnosing appendicitis. A CT scan can provide detailed cross-sectional images of the abdominal cavity, allowing for better visualization of the appendix and surrounding structures. This is particularly useful in cases where the appendix is not clearly visualized on ultrasound or where there is suspicion of a complicated appendicitis.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect as it does not provide a clear diagnostic pathway for suspected appendicitis. MRI may be useful in certain cases, but it is not the next step following inconclusive ultrasound findings.

**Option B:**
This option is incorrect as it does not provide a clear diagnostic pathway for suspected appendicitis. While a repeat ultrasound may be performed, it is not the next step following inconclusive findings.

**Option C:**
This option is incorrect as it does not provide a clear diagnostic pathway for suspected appendicitis. A plain abdominal X-ray is not sensitive for diagnosing appendicitis and would not be the next step following inconclusive ultrasound findings.

**Clinical Pearl / High-Yield Fact**
In cases of suspected appendicitis, it is essential to perform a thorough physical examination and to consider alternative diagnoses such as mesenteric lymphadenitis or ovarian torsion, particularly in females.

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