Use the following to answer question: 
-(Table: Coal Mine Pollution) Use Table: Coal Mine Pollution.The table shows the marginal social benefit and cost of various amounts of pollution from a coal mine.From the perspective of efficiency,2 tons of pollution is:
Definitions:
Thrifty Gene
A hypothetical gene that is thought to predispose individuals to efficiently collect and process food to deposit fat during periods of food abundance, theoretically offering a survival advantage during times of food scarcity.
Genetic Predisposition
The increased likelihood of developing a particular disease or condition based on a person's genetic makeup.
Mitochondrial DNA
The DNA located in the mitochondria, transmitted maternally, and used in genetic studies and evolutionary biology.
Lactase Retention
The continued production of the enzyme lactase into adulthood, allowing for the digestion of lactose found in milk; varies genetically among populations.
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