Ethanol is a chemical that can be synthetically produced from the sugars of plants, such as corn, using the fermentation reaction shown below. The reaction shows that sugar from plants can be broken down into ethanol and carbon dioxide, releasing heat.

sugar → ethanol + carbon dioxide + heat

In the United States, the sugar used to produce ethanol is commonly gained from corn—the same type of corn that is used for some foods, like corn flour, corn syrup, and corn oil. The ethanol can then be used as fuel in automobiles.

Scientists and engineers are working to develop ways to replace corn with a different plant, such as switchgrass, in the production of ethanol. This is largely because using corn to produce ethanol could cause a problem for society. Which statement describes this problem?
A.
Chemical processes that can transform corn's sugars into ethanol do not exist.
B.
Grass resources are scarce and could be used up if harvested to produce ethanol.
C.
Chemical processes that can release the chemical energy in ethanol do not exist.
D.
Corn grown for ethanol could take up field space that had been used to grow corn for food.