托福阅读中句子插入题是重要题型之一。根据托福阅读题型不同来进行专项练习，是短期提高托福阅读能力的有效方法。同学们需要多加练习哦!

　　托福阅读句子插入题：Extinction of the Dinosaurs

　　【Paragraph 5】Ir has not been common at Earth’s since the very beginning of the planet’s history. Because it　usually exists in a metallic state, it was preferentially incorporated in Earth’s core as the planet cooled and consolidated.　Ir is found in high concentrations in some meteorites, in which the solar system’s original chemical composition is　preserved. Even today, microscopic meteorites continually bombard Earth, falling on both land and sea. By measuring　how many of these meteorites fall to Earth over a given period of time, scientists can estimate how long it might have　taken to deposit the observed amount of Ir in the boundary clay. ■ These calculations suggest that a period of about one　million years would have been required. ■However, other reliable evidence suggests that the deposition of the boundary　clay could not have taken one million years. ■So the unusually high concentration of Ir seems to require a special　explanation. ■(Extinction of the Dinosaurs)

　　! Look at the four squares [■] that indicate where the following sentence could be added to the passage.

　　Consequently, the idea that the Ir in the boundary clay came from microscopic meteorites cannot be accepted.

　　Where would the sentence best fit?

　　托福阅读句子插入题答案：2

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