Final answer:
The most common action types in modern firearms are semi-automatic, pump, bolt, break, and lever, corresponding to various mechanisms of loading and ejecting ammunition.
Step-by-step explanation:
The most common action types in modern firearms are: B. Semi-automatic, pump, bolt, break, and lever. Each action type describes the mechanism by which a firearm loads, fires, and ejects a cartridge or shell. A semi-automatic weapon automatically chambers the next round after firing, ready for the next shot. A pump-action requires the shooter to manually cycle the action, usually via a fore-end slide mechanism, to eject the spent case and load a new one. A bolt-action involves manually operating the weapon's bolt to eject the spent cartridge and chamber a new round. A break-action opens at the breech, allowing cartridges to be loaded directly into the chamber(s). Lastly, a lever-action firearm features a lever that the shooter works to cycle the action.