题目解析:
B 用 porosity 定位到该段的第四句话,而 this 也预示着,前一句话也相关: Between sediment grains are spaces that can be filled with water. This pore space is known as porosity and is expressed a percentage of the total rock volume. Porosity is important for water-storage capacity...从这两句话中可以明确读到:porosity 指的是可以储水的空隙。用岩石体积的 percentage 表示,对于储水容量很重要。那么就和 B 选项的内容呼应。A 决定于 permeability of rack, 对应本段最后一句;C 和 porosity 没有直接关系;D 原文就没提到。