What is a characteristic of a break-action firearm?

A break-action firearm is uniquely designed such that the barrel is hinged, allowing it to open for loading and unloading ammunition. This characteristic is essential because it enables the shooter to easily access the chamber to load or remove cartridges, which significantly enhances safety and user convenience. Break-action firearms can include models like single-shot or double-barreled shotguns, where the opening mechanism is the defining feature.

Other firearm types may feature fixed barrels, automatic firing capabilities, or mechanisms that engage external inputs or systems to discharge, but these attributes do not align with the fundamental design characteristics of break-action firearms. The ability to open the barrel is what distinguishes this class of firearm, making option C the correct choice.