All of the following are examples of alternative energy sources except

- biofuels

- natural gas

- solar power

- hydroelectricity

Alternate energy: energy that is not popularly used and is usually environmentally sound, such as solar or wind energy (as opposed to fossil fuels).

SO ... Biofuels are the only one that is not environmentally sound. Natural gas is no greenhouse gas and is safe for the environment. Solar power is power from the sun. Hydroelectricity is the power that comes from moving water AKA dams.