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托福阅读句子插入题：the Periodic Table

2015-08-20 17:41:42来源：网络

　　【托福阅读题型：the Periodic Table句子插入题】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!

　　查看全部：托福阅读题型分类练习之句子插入题

　　托福阅读句子插入题：the Periodic Table

　　【Paragraph1】The periodic table is a chart that reflects the periodic recurrence of chemical and physical properties　　of the elements when the elements are arranged in order of increasing atomic number (the number of protons in the　　nucleus). It is a monumental scientific achievement, and its development illustrates the essential interplay between　observation, prediction, and testing required for scientific progress. In the 1800's scientists were searching for new　elements. By the late 1860's more than 60 chemical elements had been identified, and much was known about their　descriptive chemistry. Various proposals were put forth to arrange the elements into groups based on similarities inchemical and physical properties. ■The next step was to recognize a connection between group properties (physical or　　chemical similarities) and atomic mass (the measured mass of an individual atom of an element). ■When the elements　known at the time were ordered by increasing atomic mass, it was found that successive elements belonged to differentchemical groups and that the order of the groups in this sequence was fixed and repeated itself at regular intervals.　■Thus when the series of elements was written so as to begin a new horizontal row with each alkali metal, elements of　the same groups were automatically assembled in vertical columns in a periodic table of the elements. ■This table was　the forerunner of the modern table.(Development of the Periodic Table)

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

　　It was a natural Idea to break up the series of elements at the points where the sequence of chemical groups to

　　which the elements belonged began to repeat itself.

　　Where would the sentence best fit?

　　答案见下一页：

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