题型分类：文章总结题

题干分析：选择概括性的正确选项。

选项分析：

C 选项是第二段和第三段的重要信息。they slow currents and waves, seagrass beds collect deposits of rich organic sediments 对应第二段的第一句 The slowing of wave action and currents means that seagrass beds tend to accumulate sediment 也是本段的主旨句。are home to many anaerobic microorganisms 对应第三段的第一句 Since most seagrass systems are depositional environments, they eventually accumulate organic material that leads to the creation of... 也是本段的主旨句。

E 选项是第三段的重要信息，Unlike sea organisms that depend on the water column for their productivity 对应第三段的倒数第二句 In contrast to other productivity in the ocean... seagrasses are rooted plants that absorb nutrients from the sediment or substrate，seagrasses ensure high rates of productivity by taking nutrients from ocean floor sediment 对应最后一句 They are, therefore, capable of recycling nutrients into the ecosystem that would otherwise be trapped in the bottom and rendered unavailable。

F 选项是第四段的重要信息。more extreme temperatures can damage them, as can desiccation and lack of light 对应第四段的第一句 Other physical factors that have an effect on seagrass beds include light, temperature, and desiccation (drying out)。

A 选项说 the most significant being the stability of the sea bottom，文中无此信息，无中生有。

B 选项说 temperate beds accumulating sediments from within, and tropical beds collecting sediments from without，而第二段的第四句说的是 It is interesting that temperate seagrass beds accumulate sediments from sources outside the beds, whereas tropical seagrass beds derive most of their sediments from within 因此该选项与原文描述矛盾。

D 选项说 Seagrasses under weak currents tend to have higher rates of metabolism than those under strong currents，文章第三段没有此方面的比较，同时选项中说 perhaps because of differences in oxygen levels 也是文中未提及的信息。无中生有。