**Core Concept**
Turner's syndrome is a genetic disorder that affects females, causing short stature, infertility, and other physical characteristics. The underlying principle being tested is the association between Turner's syndrome and cardiac anomalies. **Congenital heart defects** are common in Turner's syndrome, particularly those affecting the left side of the heart.

**Why the Correct Answer is Right**
The most common cardiac anomaly associated with Turner's syndrome is **bicuspid aortic valve**, which is a congenital defect where the aortic valve only has two cusps instead of three. This can lead to **aortic stenosis** or **aortic regurgitation**. The **left-sided obstructive lesions** are also common, including **coarctation of the aorta**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not the most common cardiac anomaly associated with Turner's syndrome.
**Option B:** Incorrect as it is not typically associated with Turner's syndrome.
**Option D:** Incorrect because, although it can occur, it is not the most common cardiac anomaly in Turner's syndrome.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that individuals with Turner's syndrome require regular **cardiac evaluation** to detect and manage any potential cardiac anomalies.

**Correct Answer: D. Bicuspid aortic valve**