**Core Concept**
High anion gap (HAG) metabolic acidosis occurs when there is an accumulation of unmeasured anions in the blood, leading to an increased difference between the measured cations (sodium and potassium) and anions (chloride and bicarbonate). This condition is often caused by diabetic ketoacidosis, lactic acidosis, and certain ingestions.

**Why the Correct Answer is Right**
The correct answer will identify a characteristic or cause of high anion gap metabolic acidosis. High anion gap metabolic acidosis is typically associated with conditions that lead to an accumulation of acidic substances, such as lactic acid, ketones, or certain toxins. The anion gap is calculated by subtracting the chloride and bicarbonate concentrations from the sodium concentration (Na+ - (Cl- + HCO3-)).

**Why Each Wrong Option is Incorrect**
* **Option A:** This option might be incorrect if it describes a condition that typically causes normal anion gap metabolic acidosis, such as gastrointestinal loss of bicarbonate.
* **Option B:** This option might be incorrect if it describes a condition that typically causes hyperchloremic metabolic acidosis, such as renal tubular acidosis.
* **Option C:** This option might be incorrect if it describes a condition that is not typically associated with high anion gap metabolic acidosis, such as respiratory acidosis.

**Clinical Pearl / High-Yield Fact**
One important aspect of high anion gap metabolic acidosis is that it can be caused by a variety of underlying conditions, and the specific cause should be identified based on clinical presentation and laboratory results.

**Correct Answer: D.**