Which of the following best exemplifies a potential tragedy of the commons?

A) Everyone shows up at the party wearing the same pink shirt.
B) Nobody cleans the lake after pollutants are accidentally spilled in it.
C) Multiple shepherds allow their sheep to graze on a plot of land.
D) A rainforest is cut down to build housing.

When multiple shepherds allow their sheep to graze on a plot of land, each shepherd has an individual incentive to have their sheep consume as much as possible, leading to overgrazing and depletion of the land's resources. This is an example of the tragedy of the commons, where individuals acting in their own self-interest can collectively harm a shared resource.

Option A is not an example of the tragedy of the commons as it does not involve a shared resource. Option B is an example of pollution, but not the tragedy of the commons specifically. Option D is an example of deforestation, but again, not specifically related to the tragedy of the commons.