Concept:Alkanoic acids are saturated carboxylic acids, and human sweat contains propanoic acid produced by skin bacteria.Explanation:Bacteria such as Propionibacterium break down sweat components.They release propanoic acid as a metabolic end-product.This acid has the formula CH3CH2COOH.It contributes to the characteristic odour of human sweat.Answer:CH3−CH2−COOH is the correct choice.