**Core Concept**
Pulmonary plethora refers to an increased vascular markings visible on chest radiographs, indicating increased blood flow to the lungs. This condition is often associated with left-to-right shunting of blood, where oxygenated blood from the left heart is diverted to the right heart, resulting in excessive blood flow to the lungs.

**Why the Correct Answer is Right**
Total Anomalous Pulmonary Venous Connection (TAPVC) is a congenital heart defect where the pulmonary veins connect anomalously to the systemic veins or right atrium, rather than the left atrium. This results in deoxygenated blood from the lungs returning to the right heart, which then pumps it to the left heart, creating a left-to-right shunt. Consequently, the increased blood flow to the lungs leads to pulmonary plethora. The anomalous connection also leads to an increased pressure in the pulmonary veins, causing them to become enlarged and visible on chest radiographs.

**Why Each Wrong Option is Incorrect**
**Option B:** Tetralogy of Fallot (TOF) is a congenital heart defect characterized by four main features: ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. TOF typically results in decreased blood flow to the lungs, not increased, due to the pulmonary stenosis.

**Option C:** Ebstein's anomaly is a congenital heart defect where the septal and posterior leaflets of the tricuspid valve are abnormal and the right ventricle is small. This condition often leads to right-to-left shunting, resulting in decreased blood flow to the lungs.

**Option D:** Tricuspid atresia is a congenital heart defect where the tricuspid valve is completely absent or abnormally developed, preventing blood flow from the right atrium to the right ventricle. This condition also leads to right-to-left shunting, resulting in decreased blood flow to the lungs.

**Clinical Pearl / High-Yield Fact**
In patients with TAPVC, the chest radiograph may show a "snowman sign" or "figure-of-eight" sign due to the dilated pulmonary veins and the anomalous connection to the systemic veins.

**✓ Correct Answer: A. TAPVC**