Which of the following is a complication of gallstones?

The most appropriate complication of gallstones from the provided options is jaundice. Gallstones can block the common bile duct, leading to an obstruction of bile flow. When this occurs, bilirubin, a byproduct of the breakdown of red blood cells, accumulates in the blood due to the inability to be excreted through the bile. This accumulation results in a yellowing of the skin and eyes, characteristic of jaundice.

In contrast, while cirrhosis is a chronic liver condition typically associated with long-term liver damage from various causes such as chronic alcohol use or viral hepatitis, it is not a direct complication of gallstones. Pneumonia and diabetes are also unrelated complications in the context of gallstones; pneumonia is a respiratory condition, while diabetes is a metabolic disorder primarily related to insulin and glucose metabolism. Thus, the complication directly linked to gallstones due to their potential to obstruct bile flow is jaundice.