**Core Concept**
Metabolic acidosis is a condition characterized by an increase in blood acidity due to an excess of acid or a deficiency of bicarbonate ions. The body's compensatory mechanisms aim to restore acid-base balance by eliminating excess hydrogen ions or increasing bicarbonate levels.

**Why the Correct Answer is Right**
Compensation for metabolic acidosis primarily involves the kidneys, which increase the excretion of hydrogen ions and increase the reabsorption of bicarbonate ions. This process is mediated by the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system, which stimulate the release of aldosterone. Aldosterone promotes the reabsorption of sodium and water in the collecting ducts of the kidneys, which in turn increases the delivery of sodium and water to the distal tubules. Here, the sodium-hydrogen exchanger (NHE3) exchanges sodium ions for hydrogen ions, increasing the excretion of hydrogen ions and reducing the acidity of the blood. Additionally, the kidneys can also increase the excretion of ammonium ions, which help to buffer excess hydrogen ions.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is vague and does not specify the primary mechanism of compensation for metabolic acidosis.
**Option B:** While the respiratory system can contribute to compensation for metabolic acidosis by increasing ventilation and expelling CO2, it is not the primary mechanism of compensation.
**Option C:** This choice is incorrect as the liver does not play a direct role in the compensation for metabolic acidosis.

**Clinical Pearl / High-Yield Fact**
The kidneys' ability to compensate for metabolic acidosis is crucial, and failure to do so can lead to severe acid-base disturbances. It's essential to remember that the kidneys can compensate for metabolic acidosis by increasing the excretion of hydrogen ions and increasing the reabsorption of bicarbonate ions.

**Correct Answer:** D.