Finally I found the answer
<span>Alternate energy: energy that is not popularly used and is usually environmentally sound, such as solar or wind </span>energy<span>(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.</span>
