托福考试2017阅读模拟冲刺题（二十三）_第2页

　　5. 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 in petroleum-producing sediment

　　(D) a decline in the quantity of calcareous ooze on the seafloor

　　6. The "white chalk cliffs of Dover" are mentioned in line 14 of the passage to

　　(A) show where the plankton sediment first began to build up

　　(B) provide an example of a plankton buildup that scientists cannot explain

　　(C) provide an example of the buildup of plankton sediment

　　(D) indicate the largest single plankton buildup on Earth

　　7. The word "prolific" in line 17 is closest in meaning to

　　(A) fruitful

　　(B) distinct

　　(C) determined

　　(D) energetic

　　8. The word "ideal" in line 20 is closest in meaning to

　　(A) common

　　(B) clear

　　(C) perfect

　　(D) immediate

　　9. The word "it" in line 22 refers to

　　(A) biological productivity

　　(B) oil

　　(C) organic material

　　(D) petroleum

　　参考答案：CBBAA DCACC