According to the author, we are searching for alternative sources of energy. What is the most likely reason for this?

Directions: Read the passage and answer the question.

We have built up an energy intensive society, such that hundreds of daily acts are dependent on having energy at our ready command. Most of that energy comes from fossil fuels. Yet, within two centuries we will have used up nearly all of the fossil fuel that has been built up over millions of years of earth time. Furthermore, the extraction and consumption of fossil fuels is a major polluter of our environment. Our appetite for energy is seemingly insatiable. We are now searching for it in different places and using methods that inevitably upset and pollute the environment. Since fossil energy will soon be gone we are searching for alternative sources.