题型分类：否定事实信息题

题干分析：定位词dinoflagellates；利用定位词定位到第五段的第二句至最后，包含较多信息，需要结合选项逐一排除。

选项分析：

D选项说Their toxins are dangerous only to other photosynthetic organisms，而最后一句This toxin can be concentrated in such filter-feeding organisms as clams and mussels, rendering them toxic to humans，说明不仅对photosynthetic organisms，也会对人类有毒，选项中使用only太绝对了。

A选项说 They produce toxins that inhibit the growth of other organisms. 对应第二句 Some are likely toxins, such as those released by the dinoflagellates (a species of plankton) during red tides, which inhibit growth of other photosynthetic organisms. 不选。

B选项说 Each produces a very little amount of toxin. 对应倒数第二句 Although each cell secretes a minute amount of toxin. 不选。

C选项说 Their toxins can concentrate in clams and mussels. 对应最后一句 This toxin can be concentrated in such filter-feeding organisms as clams and mussels, rendering them toxic to humans. 不选。