Answer:
C.
Step-by-step explanation:
Renewable energy sources (e.g., solar energy, wind energy, hydrothermal energy) represent the most important alternative to reduce global warming effects due to the use of fossil fuels. However, the use of renewable energy sources is nowadays more expensive than those derived from fossil fuels. For example, it has been calculated that solar energy costs around 20 cents more per KWH than coal or gas. Wind energy is even more expensive than solar energy. In consequence, it is expected that in the near future renewable energy production costs decrease in order to make this type of energy source cheaper than fossil fuels.