B. oil, gas, natural gas — Fossil fuels are oil, coal, and natural gas. This is the correct answer as they are all mentioned as fossil fuels in the passage.

A. the sun, wind, water — The passage mentions that alternative sources of energy include the sun, wind, and water.

B. the sun — Plants on Earth get their energy from the sun, as stated in the passage.

A. we are looking for other alternative sources of energy — The question "What will happen when there is no oil, coal, and gas on the earth?" indicates that scientists are searching for alternative energy sources to replace fossil fuels.