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  3. They sparkle and glitter in the light. No other rocks are so hard. They are v

They sparkle and glitter in the light. No other rocks are so hard. They are v

游客2025-01-08  12
问题    They sparkle and glitter in the light. No other rocks are so hard. They are very valuable. It might cost thousands and thousands of dollars to buy just one. Most are found in the ground. The largest ore ever discovered is as big as a man’s fist. But most are tiny.
   They’re diamonds!
   For hundreds of years men have risked their lives searching for diamonds. To many the discovery of this glittering treasure has seemed more important than the discovery of new lands. Fairy stories tell of brave knights who battled fierce dragons and evil wizards to win kingdom rich with diamonds. In the Tower of Ion- don in England, there is a very special room protected by guards. There, inside a thick glass case, are jeweled crowns once worn by kings and queens. People from all over the world come to see the shimmering diamonds and other precious stones that shine from behind the glass.
   Most diamonds seem to flash with a kind of white fire. But there are diamonds that sparkle in other colors, too. Sometimes diamonds are discovered in gravel at the bottom of rivers and streams. (To get these diamonds, the gravel is sucked up through giant hoses that act like vacuum cleaners.) Diamonds are found in rivers, on land, and in great stretches of hot desert sand. A few small ones are even found or near meteorites that strike the ground from outer space.
   But most diamonds are found in rocks deep inside the diamond mines of Africa. The diamonds were made millions and millions of years ago when flaming volcanoes melted a mineral called carbon which was a part of these rocks. Gigantic earthquakes shook the rock and pressed them tightly together. The hot melted carbon in the rock squeezed at the same time--squeezed so tightly that by the time it cooled, it had changed into the lovely hard gems called diamonds.
   To get at these valuable diamond rocks, workers ride in an elevator that goes down and down into the blackness far below the ground. Tunnels connect this deep shaft with the openings--called pipes--inside the ancient volcanoes.
   When they are first dug from the mines, diamonds don’t glitter or sparkle as they do when we see them in rings or other jewelry. They look more like dull bits of glass. A man who knows all about diamonds--a diamond cutter--must cut them just right. Diamonds are so hard that nothing can cut them except the edge of an- other diamond.
   Using his diamond-edged tools, the diamond cutter carefully removes tiny pieces so that the diamond will have many sharp edges and smooth surfaces--like little windows. It is because of these shaft edges and smooth surfaces that the diamond reflects light, sparkles and flashes with tiny bursts of color, and seems almost ablaze with fire. Diamond cutters often use diamond saws. The fine powder--diamond dust--that is left after the sa- wing is done can be used in a kind of sandpaper to polish the sparking gems.
   Not all diamonds are clear enough or pretty enough or large enough to be made into jewelry. But because they are so hard, they can be used for other things, such as points for drills and needles for record player. These diamonds are called industrial diamonds. Some of them are man made. Carbon is heated until it is hot and then squeezed. If men ever learn how to make it hot enough and to squeeze it tightly enough, they will probably be able to make big diamonds. Then maybe diamonds will be cheap enough to use as buttons on your shirt or coat! (610) [br] Diamonds are so hard that only _____ can cut it.
选项 A、a man who knows all about diamonds
B、diamond-edged tools
C、a special cutter
D、diamond cutter
答案 B
解析 事实细节题。本题答案的依据在文章倒数第三段：Diamonds are so hard that nothing can cut them except the edge of another diamond．A项和D项实际上是同一概念，作为钻石切割者，没有工具，他们也无法切割钻石。C项特殊工具不准确，因此舍弃。
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