2. 外语
  3. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the

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问题 Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.
Write your answer choices in the spaces where they belong. You can either write the letter of your answer choice or you can copy the sentence.
The term "Cambrian explosion" refers to the geologically brief period during which all modern animal groups evolved.
                        Answer Choices
[A]The Cambrian period is significant because it marks the emergence of eukaryotic life-forms—organisms that have cells with true nuclei.
[B]Little is known about the stages of evolution during the Cambrian period, in part because early animals were soft bodied and could fossilize only under particular conditions.
[C]The Ediacara fossil formation provides the most information about the Cambrian explosion, while the earlier Tommotian and Burgess Shale formations give clues about Precambrian evolution.
[D]While animal fossils from before the Cambrian explosion have no modern descendants, many animals that evolved during the Cambrian explosion can be assigned to modern groups.
[E]Zoologists are awaiting the discovery of a 600-million-year-old fossil formation in order to be able to form a theory of how animal evolution progressed.
[F]Although the reasons for the rapid evolution of animals during the Cambrian period are not known, one proposed explanation is an abundance of niches with a lack of competitors.
选项
答案B, D, F
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