A.although
B.though
C.like
D.as
第1题
A.Hard although the diamond is
B.Hard as the diamond is
C.As the diamond is hard
D.How hard is the diamond
第2题
A.Hard a diamond is
B.Hard as a diamond is
C.As a diamond is hard
D.How hard is a diamond
第3题
A.Hard a diamond is
B.Hard as a diamond is
C.As a diamond is hard
D.How hard is a diamond
第4题
A.Hard although a diamond is
B.As a diamond is hard
C.Hard as a diamond is
D.How hard is a diamond
第5题
A.Diamonds.
B.Diamond dust.
C.Big diamond stones.
D.Hard steel.
第6题
____, it is quite easy to drill a hole in it with laser.
A.Hard although a diamond is
B.As a diamond is hard
C.Hard as a diamond is
D.How hard is a diamond
第7题
A.a man who knows all about diamonds
B.diamond-edged tools
C.a special cutter
D.diamond cutter
第8题
A.a man who knows all about diamonds
B.diamond-edged tools
C.a special cutter
D.diamond cutter
第9题
A.Diamond is used in cutting tools because the strong covalent bonds make it very harD
B.Graphite acts a lubricant because of the weak bonds between the layers.
C.Graphite conducts electricity because the electrons between the layers are free to move
D.Graphite has a low melting point because of the weak bonds between the layers.
第10题
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 Lon- don in England, there is a very special room protected by guards. There, inside a thick glass ease, 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--squee2ed 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 tings 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 another 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 sawing 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)
The following are the characters of diamonds EXCEPT ______.
A.they sparkle and glitter in the light
B.they are very hard
C.they are very valuable
D.they are tiny
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