Which of the following would do most to cut the global buildup of carbon dioxide over the next 30 years?

a. Elimination of all subsidies to energy use.

b. Restoration of the original tropical rain forest.

c. A tax that rises to $86 per ton of emitted carbon dioxide, as described in this chapter.

d. The trend toward rising fuel scarcity, caused by exhausting the world’s reserves of fossil fuels.