Paragraph3: One interpretation regardingthe absence of fossils during this important 100-million-year period is thatearly animals were soft bodied and simply did not fossilize. ■ Fossilization ofsoft-bodied animals is less likely than fossilization of hard-bodied animals,but it does occur. ■ Conditions that promote fossilization of soft-bodiedanimals include very rapid covering by sediments that create an environment thatdiscourages decomposition.■ In fact, fossil beds containing soft-bodied animalshave been known for many years. ■

　　13. Look at the four squares [■] thatindicate where the following sentence could be added to the passage.

　　It isrelatively rare because the fossilization of soft-bodied animals requires aspecial environment.

　　Where could the sentence bestfit?

　　14. Directions: An introductory sentence for a briefsummary of the passage is provided below. Complete the summary by selecting theTHREE answer choices that express the most important ideas in the passage. Someanswer choices do not belong in the summary because they express ideas that arenot presented in the passage or are minor ideas in the passage. This question isworth 2 points.

　　The term “Cambrian explosion” refers to thegeologically brief period during which all modern animal groupsevolved.

　　AnswerChoices

　　1. Little is known about the stages of evolution during the Cambrianperiod, in part because early animals were soft bodied and could fossilize onlyunder particular conditions.

　　2. While animal fossils from before the Cambrianexplosion have no modern descendants, many animals that evolved during theCambrian explosion can be assigned to modern groups.

　　3. The Cambrian periodis significant because it marks the emergence of eukaryotic life-forms –organisms that have cells with true nuclei

　　4. The Ediacara fossil formationprovides the most information about the Cambrian explosion, while the earlier,Tommotian and Burgess Shale formations give clues about Precambrianevolution.

　　5. Zoologists are awaiting the discovery of a 600-million-year-oldfossil formation in order to be able to form a theory of how animal evolutionprogressed.

　　6. Although the reasons for the rapid evolution of animals duringthe Cambrian period are not known, one proposed explanation is an abundance ofniches with a lack of competitors. 　　

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