**Core Concept**
Edward's syndrome, also known as Trisomy 18, is a genetic disorder characterized by an extra copy of chromosome 18. This condition is associated with various congenital heart defects due to the altered genetic expression and development of the cardiovascular system.

**Why the Correct Answer is Right**
The most common congenital heart disease associated with Edward's syndrome is a **Ventricular Septal Defect (VSD)**. This is because the extra copy of chromosome 18 disrupts the normal development of the heart, leading to the formation of a hole in the ventricular septum, which is a thin wall of tissue separating the two ventricles. The increased pressure and flow of blood through the VSD can lead to pulmonary hypertension and other complications.

**Why Each Wrong Option is Incorrect**
* **Option A:** While Hypoplastic Left Heart Syndrome (HLHS) is a severe congenital heart defect, it is not the most common association with Edward's syndrome.
* **Option B:** Atrial Septal Defect (ASD) is another type of congenital heart defect, but it is not as commonly associated with Edward's syndrome as VSD.
* **Option D:** Tetralogy of Fallot (TOF) is a complex congenital heart defect, but it is not the most common association with Edward's syndrome.

**Clinical Pearl / High-Yield Fact**
In patients with Edward's syndrome, the presence of a VSD is a strong indicator of the underlying genetic disorder, and it can guide further diagnostic testing and management.

**Correct Answer:** C. Ventricular Septal Defect (VSD).