What is a key characteristic of common resources?

Common resources are characterized by a high degree of rivalry and low excludability. This means that when one person uses a common resource, it diminishes the availability of that resource for others; this is the high degree of rivalry. For instance, consider a fishery or a public pasture: when one individual catches fish or grazes livestock, these actions reduce the amount available to others.

At the same time, common resources are often not easily excludable. This means that individuals cannot be effectively barred from accessing these resources. For example, it can be difficult to prevent someone from using a public lake for fishing or swimming, even if their usage affects the availability of that resource for others.

This characteristic leads to what is often referred to as the “tragedy of the commons,” where overuse of a resource can lead to depletion or degradation, as individuals act in their self-interest without considering the collective impact on the resource. Thus, the defining features of common resources are their high rivalry and low excludability, making option C the correct choice.