2. 外语
  3. Diamond is the hardest naturally occurring substance known. It is the most popular gemstone and because of its extreme 【C1】_____

Diamond is the hardest naturally occurring substance known. It is the most popular gemstone and because of its extreme 【C1】_____

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问题
    Diamond is the hardest naturally occurring substance known. It is the most popular gemstone and because of its extreme 【C1】______(hard), it is also used for various industrial purposes. Scientists are still 【C2】______(sure)of the exact process by which diamonds are naturally formed, but it is certain that both extreme heat and enormous pressure are needed. It is, therefore, likely that diamonds were formed far【C3】be______the Earth’s surface where these conditions exist. The first synthetic diamonds were successfully produced in the 1950s, but the best and largest stones are still those created by nature.
    The word ’ diamond’ comes from the Greek ’ adamas’ , which means invincible, but the first definite reference to diamonds occurs in Roman literature of the first century A. D. The diamonds known to the Romans came from India, which was the only 【C4】______(supply)of the stones until the eighteenth century. In 1762, diamonds were discovered in Brazil, and then in 1866 in South Africa, the main source of diamonds in the world today.
    The idea that men should give diamonds to the women they 【C5】______is quite new. It was invented in the last century by De Beers, the company that owns the South African diamond mines. The idea that ’diamonds are forever’ does not hold water either. Although diamonds are very hard, they can be【C6】dam______.
    The largest of all known diamonds was the Cullinan. It was【C7】disc______in South Africa in 1905 and given to Edward VII, king of Great Britain. It was cut into smaller stones, the largest of which—and still the largest cut diamond in 【C8】______(exist)—is called the Star of Africa.
    There have been a lot of diamond thefts in recent years, but scientists can now mark stones to show who own them. Usually this mark is 【C9】______(visible), so thieves can’t tell if a diamond is marked. 【C10】O______the people who know how to make the mark appear can tell whether a diamond is marked or not.
【C9】
选项
答案invisible
解析 (由后文提到的“所以如果钻石被打上了标记，小偷也看不出来”，可知，空格处表示的是钻石上的标记看不见，即“invisible”。)
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C类竞赛（非英语专业本科）

大学生英语竞赛（NECCS）

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