通过同位素16和18判断冰川周期的文章。
66. It can be infered from the passage that calsium carbonate shells
D. contain radioactive material that can be used to determine a sediment's isotopic composition
E. refelct the isotopic composition of the water at thetime the sheels were formed
答案是E,我觉得D也对,因为shells含同位素16和18,就是根据对shells进行radioactive分析判断16和18的含量从而决定当年是否属于冰川年。那为什么D错?