Question: Some of the new cars being made can run on a renewable fuel that is made mostly from corn. Scientists are developing even more renewable fuels to replace gasoline. Why are renewable fuels most likely becoming more important?

  Options: 
 A. Renewable fuels release less energy.
 B. Car fuel tanks are being made smaller.
 C. The demand for gasoline is decreasing.
 D. Nonrenewable fuel supplies are limited. 
Answer: D