Read the Paragraph Below and Answer the Questions That Follow

Read the paragraph below and answer the questions that follow.
(1) Energy sources can be divided into two groups: nonrenewable sources and renewable sources. (2) The first group, nonrenewable sources, includes the energy sources that are in finite supply and will eventually be depleted. (3) Fossil fuels, which include coal, petroleum, and natural gas, are in this category. (4) They are obtained from deposits in the earth that were formed from living matter during previous geologic eras. (5) When these deposits have been emptied, these energy sources will no longer be available. (6) The second group contains renewable energy sources. (7) Energy produced by wind, water, the sun's rays, and the heat of the Earth, for example, will always be available because these sources continuously regenerate as they are consumed. On what basis does the writer classify energy sources?

A) amount of the supply
B) cost of use
C) intensity of power generated