26. By saying “one of the harder challenges,” the author implies that___

26.【答案】[A] forests may become a potential threat

【解析】细节理解题，答案在文中第一段。第三句“The climate change we are hastening could one day leave us with forests that emit more carbon than they absorb.”为本段的主题句，指出我们人类所造成的气候变化问题最终会使得森林排放而非吸收更多的二氧化碳，即森林可能反而会威胁气候的恶化和人类的生存。故选择A项。