**Core Concept**
Fallot's tetralogy is a congenital heart defect characterized by four key anomalies: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. It results from a combination of genetic and environmental factors during fetal development.

**Why the Correct Answer is Right**
The manifestation of Fallot's tetralogy is primarily due to the obstruction of blood flow from the right ventricle to the pulmonary artery, leading to cyanosis. This cyanosis is caused by the mixing of oxygenated and deoxygenated blood in the right ventricle, which is then pumped to the systemic circulation. The overriding aorta allows blood to bypass the pulmonary circulation, further contributing to the cyanosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the manifestation of Fallot's tetralogy. The cyanosis associated with this condition is not primarily due to anemia.
* **Option B:** While clubbing can be a feature of various cyanotic heart diseases, it is not a specific manifestation of Fallot's tetralogy.
* **Option C:** This option is incorrect as the cyanosis in Fallot's tetralogy is not primarily due to a right-to-left shunt.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the cyanosis in Fallot's tetralogy can be exacerbated by increased pulmonary vascular resistance, such as in the presence of a pulmonary embolism. This can lead to a sudden increase in cyanosis, which is a medical emergency.

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