Which of the following is an example of a restricted item?

Firearms are considered a restricted item because their possession, distribution, and use are heavily regulated by law due to the potential risks associated with their misuse. Laws surrounding firearms often require permits, background checks, and specific storage conditions to ensure public safety. The classification of firearms as restricted items reflects society's efforts to control access and prevent violence, making this an essential aspect of law and order.

In contrast, the other items listed may have varying regulations but typically do not carry the same level of restriction. Soil, for instance, may be subject to specific regulations in certain contexts (like transporting across state lines) to prevent ecological harm, but it is generally not treated as a restricted item. Dog fur does not usually have defined restrictions unless tied to particular wildlife laws, and while medication can be regulated, it typically falls under guidelines rather than outright restrictions unless it involves controlled substances. Therefore, firearms stand out clearly as items that require strict regulation due to their inherent risks.