Which of the following cannot be sold legally?

Sawed-off shotguns are considered illegal to sell in many jurisdictions because they fall under specific regulations that classify them as highly restricted firearms due to their design and potential for concealment. The legal framework typically imposes stringent controls on weapons that have shorter barrels than what is allowed for standard shotguns, primarily to prevent their use in criminal activities.

In contrast, hunting rifles and handguns can be sold legally, provided they comply with existing laws, including background checks and necessary permits for the purchasers. These types of firearms are generally more accepted in regulated markets, as they serve legitimate purposes such as sport shooting and personal defense.

Thus, the correct choice identifies sawed-off shotguns as a category of firearm that is often illegal to sell, highlighting the distinction between various types of firearms and the legal constraints placed upon them.