The fundamental cause of monopoly is a. incompetent management in competitive firms. b. barriers to entry. c. the zero-profit feature of long-run equilibrium in competitive markets. d. advertising.

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Combining the emissions released by fossil fuel burning and  the carbon released via land use change, we get a total of 8.7 gt. since the problem states that the oceans "take up" or sequester  2.4 gt carbon  per year, we subtract that value from 8.7 gt, leaving us with 6.3 gt of carbon. since the problem states that 3.4 gt carbon dioxide emissions end up in the atmosphere, the "missing sink" of carbon takes up 2.9 gt, a value we got by subtracting the 3.4 gt amount recorded from the 6.3 gt carbon left available after the oceans sequester the carbon dioxide. 

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