139. Read the following passage, then answer the question below.

In 1968, the ecologist Garrett Hardin published an essay that gave a name to a familiar problem. Imagine a pasture open to all herders in a village. Each herder gains the full benefit of adding one more animal, but the cost of overgrazing is shared by everyone. A rational herder will therefore add animals, as will every other, and the pasture will eventually be destroyed. Hardin called this the tragedy of the commons, and he concluded that shared resources must be either privatized or controlled by the government.

The essay shaped debates about fisheries, forests, and pollution, yet Elinor Ostrom, a political scientist, found that its premise was often wrong. Studying communities around the world, from Swiss mountain villages that have shared alpine meadows for centuries to groups of irrigators in Nepal and Spain, she discovered that many communities manage common resources successfully without either privatization or state control. They did so by establishing clear boundaries about who may use the resource, rules adapted to local conditions, ways of monitoring use, and graduated penalties for those who break the rules. The herders in Hardin's story, in other words, are not trapped, since they can talk to one another and agree on limits.

Ostrom did not claim that commons always succeed. Her work showed that cooperation tends to fail when groups are large, when outsiders can enter freely, or when users cannot see each other's behavior. Open-ocean fisheries and the atmosphere, where these conditions hold, remain difficult cases. Her contribution was to show that the outcome depends on institutions rather than being fixed by human nature. In 2009, she became the first woman to receive the Nobel Prize in Economic Sciences.

Which sentence best expresses the main point of the last paragraph's closing idea that the outcome 'depends on institutions rather than being fixed by human nature'?