**Core Concept**
The question is testing the student's knowledge of the underlying causes of pleural effusion, which is the accumulation of excess fluid between the layers of the pleura. This condition can result from various pathological processes, including cardiac, pulmonary, and hepatic diseases. The correct answer requires an understanding of the most common etiologies of pleural effusion.

**Why the Correct Answer is Right**
Left ventricular failure is the most common cause of pleural effusion due to the increased pressure in the pulmonary veins, which leads to fluid leakage into the pleural space. This condition is often associated with congestive heart failure, where the left ventricle is unable to pump blood efficiently, resulting in fluid accumulation in the lungs and pleural space. The increased hydrostatic pressure in the pulmonary capillaries causes fluid to leak into the interstitial tissue and eventually into the pleural space.

**Why Each Wrong Option is Incorrect**
**Option A:** Cirrhosis can cause pleural effusion, but it is not the most common cause. Cirrhosis leads to fluid accumulation in the peritoneal cavity (ascites), which can track up to the pleural space, but this is less common than left ventricular failure.
**Option C:** Pulmonary embolism can cause pleural effusion, but it is not the most common cause. The effusion is usually small and occurs in response to pulmonary infarction.
**Option D:** Pneumonia can cause pleural effusion, particularly if it is complicated by a parapneumonic effusion, but it is not the most common cause.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the most common cause of pleural effusion is left ventricular failure, and this condition should be considered in patients presenting with dyspnea and pleural effusion. A key diagnostic clue is the presence of bilateral effusions, which are more commonly seen in heart failure.

**✓ Correct Answer: B. Left ventricular failure**