**Core Concept**
Congenital Diaphragmatic Hernia (CDH) is a condition characterized by the abnormal development of the diaphragm, allowing abdominal organs to herniate into the thoracic cavity. Accurate diagnosis is crucial for timely management and prognosis. Clinical tests play a vital role in confirming the diagnosis.

**Why the Correct Answer is Right**
The correct answer involves a combination of clinical and radiological tests to diagnose CDH. Chest X-ray is the initial imaging modality used to visualize the diaphragm and identify the presence of abdominal contents in the thoracic cavity. Ultrasound is another useful tool, especially in neonates, to assess the diaphragmatic defect and associated anomalies. Echocardiography may be performed to evaluate cardiac function and rule out associated cardiac anomalies. Prenatal ultrasound is also essential for diagnosing CDH in the fetal period.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not provide a definitive diagnostic test for CDH. While a CT scan may provide detailed images of the diaphragm and abdominal contents, it is not typically used as a first-line diagnostic tool due to radiation exposure concerns.

**Option B:** This option is incorrect as it is not a specific diagnostic test for CDH. A complete blood count (CBC) may be performed to evaluate for signs of infection or inflammation but does not aid in the diagnosis of CDH.

**Option C:** This option is incorrect as it is not a diagnostic test for CDH. A chest CT scan may be used in some cases to evaluate the size of the diaphragmatic defect and assess for associated anomalies, but it is not a primary diagnostic tool.

**Clinical Pearl / High-Yield Fact**
In cases of suspected CDH, it's essential to perform a thorough physical examination, including palpation of the chest and abdominal cavities, to identify any abnormalities. A high index of suspicion is required, especially in neonates, to ensure timely diagnosis and management.

**Correct Answer:** A, B, C. Chest X-ray, Ultrasound, Echocardiography, Prenatal ultrasound.