**Core Concept**
The total body water (TBW) is divided into two main compartments: intracellular fluid (ICF) and extracellular fluid (ECF). The ECF compartment further divides into plasma and interstitial fluid. The ECF is the fluid outside the cells, which plays a crucial role in maintaining blood pressure, facilitating the transport of nutrients and waste products, and maintaining acid-base balance.

**Why the Correct Answer is Right**
The best value for ECF is approximately 20% of the total body weight in adults, which is roughly 12-14 liters in a 70 kg person. This value can be calculated using the formula: ECF = TBW - ICF. The ICF is approximately 60% of the total body weight, leaving 20% for the ECF. The ECF is further divided into plasma (approximately 5% of the total body weight) and interstitial fluid (approximately 15% of the total body weight).

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, so we cannot evaluate its correctness.
* **Option B:** This option is also not provided, so we cannot evaluate its correctness.
* **Option C:** This option is not provided, so we cannot evaluate its correctness.

**Clinical Pearl / High-Yield Fact**
In clinical practice, it is essential to understand the distribution of body water compartments to accurately assess fluid status in patients. The ECF compartment is often used as a reference point to estimate the severity of dehydration or edema.

**Correct Answer: D.**