**Core Concept**
Aortic regurgitation is characterized by the backflow of blood from the aorta into the left ventricle during diastole, leading to an increased volume load on the left ventricle. This condition can cause various types of murmurs due to the altered hemodynamics.

**Why the Correct Answer is Right**
The murmur of aortic regurgitation is typically a diastolic murmur, best heard at the left sternal border. It is caused by the rapid backflow of blood from the aorta into the left ventricle, creating a high-velocity jet of blood that can cause turbulence and vibration of the ventricular wall. This murmur is often described as a low-pitched, blowing murmur that radiates to the carotids.

**Why Each Wrong Option is Incorrect**
* **Option A:** While aortic stenosis is typically associated with a systolic ejection murmur, it can also cause a diastolic murmur due to the increased pressure gradient across the aortic valve during diastole. However, this is not a characteristic murmur of aortic regurgitation.
* **Option B:** The murmur of mitral regurgitation is typically a systolic murmur, best heard at the apex, and is caused by the backflow of blood from the left ventricle into the left atrium during systole.
* **Option C:** The murmur of pulmonary regurgitation is typically a diastolic murmur, best heard at the left upper sternal border, and is caused by the backflow of blood from the pulmonary artery into the right ventricle during diastole.

**Clinical Pearl / High-Yield Fact**
In patients with aortic regurgitation, the murmur may be accentuated by standing, which increases the volume of blood returned to the left ventricle and increases the pressure gradient across the aortic valve during diastole.

**Correct Answer:** B.