单选题 An overwhelming richness of vegetation may have caused the level of oxygen, to rise above today's ______ , with a corresponding depletion of carbon dioxide.
【正确答案】 A
【答案解析】[分析] 名词辨析 A．concentration集中，浓缩，浓度；B．saturation饱和，饱和度；C．satiation饱食，饱满，厌腻；D．plenitude充分；因此A为答案。