Answer to Question 1
Ethanol is a gasoline additive that can reduce the amount of oil used, however it is a hydrocarbon, so burning it produces carbon dioxide, however it is equivalent to the carbon dioxide absorbed by the plant during growing, so the net effect is carbon neutral in the long term. Negative impacts include agricultural land taken out of production for food, water and fertilizer requirements; single crop farming requires use of increased pesticides, and there can be loss of wildlife habitat.
Answer to Question 2
A barrage dam traps water from incoming tides behind and uses it to generate power by releasing the water through turbines.
