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题库 / Prep2007E2-SC-83
The number of plant and animal species that humans are known to have forced to extinction in the last half millennium is over 800.
humans are known to have forced to extinction
humans are known as having forced to become extinct
humans are known for forcing to become extinct
are known that humans forced to become extinct
are known as having been forced to extinction by humans
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1、be known as +n. ; be known to do ; be known for doing ;排除BDE;
2、the number of单数， are known复数错误，排除DE；
3、to become extinct没有 to extinction更优。
DE的that引导的are known修饰的主语是species吧。。不能靠单复数排除吧
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