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一篇TPO的阅读： TheCambrian explosion 寒武纪大爆发
11. Sidneyia is an example of
A a relative of Anomalocaris and Wiwaxia
B. a previously unknown Burgess Shale animal
C. an extince member of a currently existing category of animals
D. an animal that cannot be assigned to any modern animal group.
正确答案是C， 为什么B不可以。

出处为第六段
A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides reapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft\bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative of a previously unknown group of arthropods(a category of animals that includes insects, spiders, mites, and crabs)