单选题
According to the passage, the most dramatic change to the oceans caused by plankton during the Cretaceous period concerned
A、
( the depth of the water
B、
( the makeup of the sediment on the ocean floor
C、
( the decrease ill petroleum-producing sediment
D、
( a decline ill the quantity of calcareous ooze on the seafloor
【正确答案】
B
【答案解析】
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