c. common resources are rival in consumption. In the tragedy of the commons, William Forster Lloyd presented the example of a common resource being over used and destroyed because for any individual abusing the resource, they gained a benefit while the damage to the resource was paid by everyone. So let's look at the available options and see what makes sense, or doesn't make sense. a. people consider the value of resources in the future more than in the present. * If this were true, the there wouldn't be a tragedy of the commons. So this is an incorrect answer. b. markets do not account for the presence of property rights. * The tragedy of the commons doesn't involve property rights. EVERYONE in the community is allowed to use the commons. The problem is irresponsible overuse of the common resource. So this is also an incorrect answer. c. common resources are rival in consumption. * This is the correct answer. The concept of Rivalry is where a common resource can not be simultaneous consumed by multiple users, or if the consumption of a resource decreases its utility to another consumer. In the tragedy, if one person grazes (consumes) more than their fair share, the commons gets over grazed and over time stops producing. Each person who's overgrazing does get a tangible short term benefit for doing so, but everyone has to pay the cost. d. government does not efficiently allocate society's scarce resources. * This is also a wrong answer. It's true that the commons could be regulated by the government, but then it would no longer be the commons.