**Core Concept**
Transudative pleural effusions are characterized by a low protein content and occur when there is an imbalance between the hydrostatic and oncotic pressures in the pleural space, leading to fluid accumulation. This is often due to conditions that increase hydrostatic pressure or decrease oncotic pressure in the pulmonary capillaries.

**Why the Correct Answer is Right**
The correct answer is a cause of transudative pleural effusion because it increases hydrostatic pressure in the pulmonary capillaries, leading to fluid accumulation in the pleural space. This condition involves left-sided heart failure, which increases the pressure in the left atrium, subsequently increasing the pressure in the pulmonary veins and capillaries. As a result, fluid leaks into the pleural space, causing a transudative effusion.

**Why Each Wrong Option is Incorrect**
**Option A:** Chylothorax is a cause of exudative pleural effusion, not transudative. Chylothorax involves the leakage of lymphatic fluid, which is rich in proteins and lipids, into the pleural space.

**Option B:** Rheumatoid arthritis is a systemic inflammatory disease that can cause exudative pleural effusions due to the inflammatory process and the release of various cytokines and enzymes, which increase the permeability of the pleural space.

**Option C:** Pulmonary embolism can cause a parapneumonic effusion, which is an exudative effusion that develops in the context of pneumonia.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the distinction between transudative and exudative pleural effusions is crucial for determining the underlying cause and guiding management.

**Correct Answer:** A. Chylothorax.