The correct answer is - c. renewable energy.
There's lots of focus and investing in the renewable energy sources because they are seen as the future in the energy usage. There's multiple reasons for this, protection of the environment, reducing pollution, improving air quality and thus human health, and on top of it all, this type of energy is not renewable, thus can not be spent, while the fossil fuels that are still dominating have limited reserves that will eventually run out, and also are causing lot of damage to the environment and human health. Over the past decade there's a steady growth in the usage of this types of energy, and it is expected that this trend will continue and that eventually will totally replace the fossil fuels.
