**Core Concept**
High anion gap metabolic acidosis (HAGMA) is a type of acid-base disorder characterized by an increased anion gap due to the accumulation of unmeasured anions, leading to a decrease in bicarbonate levels. This condition can result from various causes, including lactic acidosis, ketoacidosis, and certain toxic ingestions.

**Why the Correct Answer is Right**
The correct answer is associated with the accumulation of lactate, a key unmeasured anion responsible for the increased anion gap. Lactic acidosis occurs when there is an imbalance in aerobic and anaerobic metabolism, leading to the production of excess lactate. This condition can be caused by factors such as tissue hypoxia, sepsis, or certain medications like salicylates and ethylene glycol.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because diabetic ketoacidosis (DKA) is a specific type of metabolic acidosis characterized by a high anion gap, but it is not the only cause.
* **Option B:** This option is incorrect because chronic kidney disease (CKD) can lead to a non-anion gap metabolic acidosis, typically due to the loss of bicarbonate in the urine.
* **Option C:** This option is incorrect because gastrointestinal (GI) losses, such as seen in diarrhea, typically lead to a non-anion gap metabolic acidosis.

**Clinical Pearl / High-Yield Fact**
A key feature of HAGMA is the presence of an increased anion gap, which can be calculated as the difference between the measured sodium and the sum of chloride and bicarbonate levels. This calculation can help distinguish HAGMA from non-anion gap metabolic acidosis.

**Correct Answer:** D. Lactic acidosis is a common cause of high anion gap metabolic acidosis.