What does the term "firearm" encompass?

The correct choice is that the term "firearm" encompasses all weapons that expel a projectile through combustion or explosive force. This definition is comprehensive and aligns with the legal and technical understanding of firearms. Firearms operate on the principle of igniting a propellant (such as gunpowder) to generate gas that pushes a projectile through a barrel, whether it is a handgun, rifle, or shotgun.

This broad definition is essential for regulatory and safety purposes, as it includes a wide range of weapons that function in this manner, thereby ensuring laws and standards can address any weapon that meets this criterion. Other options presented are too narrow in scope; for instance, limiting the definition to only handguns and rifles or only rifles and shotguns excludes other types of firearms like muzzleloaders or certain types of pistols. Additionally, non-lethal weapons such as BB guns are typically classified separately and may not always function using traditional explosive forces that define firearms. Thus, the correct answer captures the full spectrum of what a firearm includes under legal definitions.