依存

環境保護のために、化石燃料への ___ を減らすべきだ。

The correct answer is 「依存」(いそん / いぞん), meaning "dependence" or "reliance." The sentence suggests that for environmental protection, we should reduce our "dependence" on fossil fuels, aligning with the global movement towards sustainable energy. 「提供」(ていきょう) means "provision" or "supply"; one does not reduce the provision *to* fossil fuels. 「貢献」(こうけん) means "contribution"; one contributes *to* something, not *to* fossil fuels in a way that needs reducing for environmental reasons. 「要求」(ようきゅう) means "demand" or "request"; while demand for fossil fuels exists, the direct relationship with "への" (to/on) makes 依存 more fitting for the state of reliance.

正解は「依存（いそん/いぞん）」です。「化石燃料への依存を減らす」は、「化石燃料に頼る度合いを減らす」という意味で、環境保護の文脈に最も合致します。「提供」は差し出すこと、「貢献」は力を尽くすこと、「要求」は求めることで、いずれも文脈に合いません。