木材、煤炭、石油和天然气都是不同种类的燃料。

Wood, coal, oil, and gas are all different kinds of ___fuel.

燃烧化石燃料会向大气中释放有害气体。

Burning fossil ___fuel releases harmful gases into the atmosphere.

减少燃料消耗有助于保护环境。

Reducing ___fuel consumption helps protect the environment.