语法与词汇 8.Some biologists argue that each specifically human trait must have arisen gradually and erratically, and that it is therefore difficult to isolate definite______in the evolution of species.
【正确答案】 D
【答案解析】本题考查名词辨析。A项“波动,变动,起伏现象”;B项“显示,表现”;C项“倾向,素质,易染病体质”;D项“里程碑,时间表”。句意为:某些生物学家指出,每种特定的人类特征都是逐渐地、不规则地产生的,因此,很难分离出物种进化过程中明确的(重大标记)。因此答案为D选项。