American paleontologists David Raup and John Sepkoski, who have studied extinction rates in a number of fossil groups, suggest that episodes of increased extinction have recurred periodically, approximately every 26 million years since the mid-Cretaceous period. The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes. The possibility that mass extinctions may recur periodically has given rise to such hypotheses as that of a companion star with a long-period orbit deflecting other bodies from their normal orbits, making some of them fall to Earth as meteors and causing widespread devastation upon impact.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
○Based on their studies of extinction rates of numerous fossil groups, paleontologists David Raup and John Sepkoski have determined that mass extinctions occur about every 26 million years.
○David Raup and John Sepkoski studied extinction rates of numerous fossil groups and suggest that mass extinctions during the Cretaceous period continued for 26 million years.
○Studies that paleontologists David Raup and John Sepkoski conducted of various fossil groups have revealed that extinction rates have increased over the past 26 million years.
○The studies conducted by paleontologists David Raup and John Sepkoski of the fossil remains of species suggest that the extinction rate of species started to increase by the middle of the Cretaceous period.
本题的题干为Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
从题干信息中可以判断出,本题主要考查学生对于句子 essential information即主要信息的
题干中所说的 essential information是什么呢?从英语语言学和托福考查的角度来说, essential information指:句子主干和逻辑关系。即当一个句子只有一套主干的时候,提取主干就是考查点，当句子中出现分句的时候,分句和主句之间的关系是考查点。
He refused to develop projection technology, reasoning that if he made and sold projectors,
then exhibitors would purchase only one machine-a projector-from him instead of a lot.
It is significant that the earliest living things that built communities on these islands are
examples of symbiosis, a phenomenon that depends upon the close cooperation of two or more
forms of life and a principle that is very important in island communities.