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Seagrass beds under the influence of strong currents tend to have many of the lighter particles, including seagrass debris, moved out, whereas beds in weak current areas accumulate lighter detrital material.
海草床在强洋流的影响下，往往会有许多较轻的颗粒，包括海草碎屑，被移走，而弱洋流区的海草床则会积聚较轻的碎屑物质。

Light particles and debris collect in some seagrass beds but are washed out of those affected by strong currents.（those指前文颗粒碎片聚集的seagrass beds）
较轻的颗粒和碎片聚集在一些海草床上，但被强洋流冲走
与原文划线部分语义重合，因此该题选择A选项

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