**Core Concept:** Amoebiasis is an infectious disease caused by the protozoan parasite Entamoeba histolytica. The infection can lead to diarrhea, abdominal pain, and in severe cases, extraintestinal manifestations like liver abscess or pneumonia. Diagnosis of amoebiasis involves identifying the parasite in stool samples and/or demonstrating the cyst stage.

**Why the Correct Answer is Right:** The correct answer, **C. Stool examination**, is the preferred method for diagnosing amoebiasis. Stool examination techniques include wet mount, concentration methods (formalin-ether, sucrose gradient), and specialized staining methods (such as Ziehl-Neelsen or modified trichrome stain). These methods help in identifying the presence of Entamoeba histolytica cysts and/or trophozoites in the patient's stool sample.

**Why Each Wrong Option is Incorrect:**

A. **Blood tests (serology)**: Although serologic tests can detect antibodies against Entamoeba histolytica, they are not specific to amoebiasis, as they can cross-react with other protozoan infections. They are not the primary diagnostic tool.

B. **Imaging studies (X-ray, ultrasound, CT scan)**: Imaging studies are useful in detecting extraintestinal complications, but they cannot directly identify the causative organism or confirm the presence of Entamoeba histolytica in the stool sample.

D. **Clinical examination**: A clinical examination alone is not sufficient for diagnosing amoebiasis, as it lacks the ability to detect the pathogen directly.

**Clinical Pearl:**

Diagnosing amoebiasis requires direct identification of the parasite in the stool sample. Stool examination remains the gold standard, while other tests serve as complementary tools to support the diagnosis. Collaboration between clinical suspicion, imaging findings, and parasite identification is crucial for accurate diagnosis and appropriate management of the patient.