Which of the following is a cause of metabolic acidosis with normal anion gap?

Metabolic Acidosis Normal anion gap acidosis (low serum HCO3 but normal anion gap) is caused by excess bicarbonate loss from either the gut (diarrhea) or kidney (renal tubular acidosis). An elevated or so-called positive anion gap suggests the presence of another unmeasured anion Ref Davidson 23rd edition pg 364