**Core Concept**
The Light's criteria are used to differentiate between transudative and exudative pleural effusions. Exudative pleural effusions are caused by conditions such as malignancy, infection, or inflammation, which lead to increased vascular permeability and fluid leakage into the pleural space.

**Why the Correct Answer is Right**
To identify an exudative pleural effusion, the Light's criteria require that at least one of the following conditions be met: a pleural fluid protein-to-serum protein ratio of > 0.5, a pleural fluid lactate dehydrogenase (LDH) level that is > 2/3 of the upper limit of normal for the patient's serum LDH level, or a pleural fluid LDH-to-serum LDH ratio of > 0.6. These criteria are used to distinguish exudative effusions from transudative effusions, which are caused by conditions such as heart failure or cirrhosis.

**Why Each Wrong Option is Incorrect**
*Option A:* This option is not provided.
*Option B:* This option is not provided.
*Option C:* This option is not provided.
*Option D:* This option is not provided.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the Light's criteria are not perfect and may not always accurately distinguish between transudative and exudative pleural effusions. However, they are a useful tool in the clinical assessment of pleural effusions and can help guide further diagnostic testing.

**Correct Answer:** A.