Which types of guns are prohibited from being sold legally?

The correct choice highlights specific categories of firearms that are designated as illegal to sell under federal law, particularly in the United States. Sawed-off shotguns, short barreled rifles, and fully automatic machine guns are all types of firearms that fall under strict regulations established by the National Firearms Act (NFA) of 1934 and subsequent legislation.

Sawed-off shotguns are considered dangerous because their reduced barrel length can make them easier to conceal and more effective in close-quarters confrontations. Short barreled rifles share similar concerns regarding their length and maneuverability. Fully automatic machine guns, capable of firing continuously with a single trigger pull, are heavily regulated due to their potential for mass casualties and the challenges they pose for law enforcement.

Each of these firearm types is subject to stringent licensing and registration requirements, effectively making their sale illegal without compliance to these regulations. This understanding is crucial for anyone involved in the auctioning of firearms, as selling prohibited types could lead to severe legal consequences.

In contrast, the other options consist of firearm categories that are typically legal to sell under specific regulations and conditions, reflecting the importance of knowing which firearms are regulated and how they can be marketed legally.