2020年军队职称英语《理工B类》模拟练习5

　　Snowflakes

　　You've probably heard that no two snowflakes are alike. Of course, nobody has ever confirmed that statement by examining every one of the estimated one septillion snowflakes that drift to Earth each year. still, Kenneth Libbrecht, a professor at the California Institute of Technology, is confident that the statement is true.

　　Snowflakes aren't flaky, says Libbrecht. At their basic level, they're crystalline. The lattice of every snowflake is six-sided in shape. The simplest snow crystals are six-sided flat plates and six-sided columns. Such crystals are common in places where the air is extremely cold and dry. Snow crystals acquire their special beauty when their simple six-sided symmetry blossoms. Under the right conditions, each of the six corners of a crystal sprouts what is called an arm. In a matter of minutes, the arms can become highly ornate and give the crystal a star like appearance.

　　Several factors in the environment affect the shape and growth rate of a snow crystal. One factor is humidity. Crystals grow faster and in more intricate shape as humidity increases. A second factor is air temperature. A snowflake is born when several molecules of water vapor in a could land on a speck of dust and freeze to form a simple crystal. As the young crystal bops around in the cloud, it passes through air pockets of varying temperatures. If the crystal passes through a pocket of air that is, says,—15 degrees Celsius, it will grow quickly and sprout six arms, says Libbrecht. If the crystal is then tossed into a warmer pocket, one about-10℃, the arms' tips will stop growing quickly and form six-side plates. If the crystal then drifts into an even warmer pocket of about -℃, its top and bottom will grow more quickly than its sides and become more column like in shape.

　　In the course of its life span, a snow-crystal might flutter through many warmer and colder pockets, acquiring a complicated and unique growth history. Such a history will give rise to a snowflake that is unlike any other. Each arm on the snowflake will look exactly like every other one, but the crystal itself will be one of a kind.

　　Using his cooling tanks, Libbrecht has learned how to create snow crystals of different shapes—plates, colhuns, needles etc. Libbrecht has even refined his techniques so that he can make crystals that look highly similar to one another. Still, he lacks the control to manufacture identical twin snowflakes. A slight difference in humidity and temperature can upset the growth profile of a crystal.

　　1. What does Professor Libbrecht believe to be true?

　　A. No two snowflakes are exactly the same in shape.

　　B. Somebody has examined all the snowflakes that on Earth.

　　C. The statement that no two snowflakes are alike is confirmed.

　　D. None of the above.

　　2. What do the simplest snow crystals look like?

　　A. They have six columns.

　　B. They are flaky.

　　C. They are cubic in shape.

　　D. They are six-sided.

　　3. What are the factors that affect the shape and growth rate of a snow crystal?

　　A. Humidity and temperature.

　　B. Water and falling speed.

　　C. Air and altitude.

　　D. Both B and C

　　4. It can be felt from the description in the 2nd paragraph that the author

　　A. admires the beauty of the snowflakes.

　　B. dislikes the changing growth history of the snowflakes.

　　C. has a particular feeling for those flower-like crystals.

　　D. likes to compare snowflakes to the stars in the sky.

　　5. Libbrecht is not able to

　　A. create snow crystals of different shapes.

　　B. make crystals that look similar to one another.

　　C. create snowflakes that are exactly alike.

　　D. refine his techniques.

　　答案与题解 :

　　1. A第一段的第一句说，没有两片雪花是同样的，昀后一句说 Libbrecht … is confident that the statement is true。这里的 statement指的就是“ no two snowflakes are alike”这句话。所以 A是正确选项。

　　2. D 第二段的第二句、第三句提供了答案。

　　3. A第三段第二句和第四句中提到了 One factor is humidity … A second factor is air temperature。所以 A是正确的答案。

　　4. A第二段描述雪花的形成过程时，用了好几个赞美的词语和句子，如 special beauty, six-sided symmetry blossoms，highly ornate等。所以，选项 A是恰当的。

　　5. C 昀后一段告诉我们， Libbrecht可以制造不同形状的雪花。他还改进了制造技术，能制造出极为相似的雪花，但还制造不出完全相同的雪花。所以 C是正确答案。

　　译文：

　　雪 花

　　你可能听说过没有两片雪花是完全相同的。当然，没有人曾经检查过每年飘落在地球上的数以万亿计的雪花来证实这一说法。然而，加州技术学院的Kenneth Libbrecht教授仍相信这一说法的真实性。

　　Libbrecht说，雪花并不是片状的。它们在基础阶段是结晶状的。每一片雪花的晶格都是六边形的。最简单的雪晶体是六边的扁平碟状和六边的柱状。这种晶体在极寒极干的地方十分普遍。当这种简单的六边对称形状发生变化时，雪晶体就拥有了它们独特的美丽之外。在适当的条件下，结晶体的每个角都向外伸长，形成臂状物。在大约几分钟的时间内，这些臂状物变得非常华美，结晶体也变得像星星般闪闪发亮。

　　环境中的几个因素影响了雪晶体的形状及形成速度。其中之一是湿度。当湿度增加时，晶体变化得更快并且形成更为复杂的形状。另一个因素是气温。云里的水蒸气分子集结在尘埃上，冷凝形成简单的晶体，此时，雪花就诞生了。初形成的晶体在云里四处碰撞，穿过不同Libbrecht说，当这些晶体遇到大约零下15度的空气团时，它们就会快速变化，伸长出六个臂状物。这时，如果晶体遇到一个温度更高的空气团(比如零下10度)，这些臂状物的尖端就会很快停止伸长，形成碟状的六边形。这时，如果遇到温度更高的空气团(比如零下5度)，它的顶部和底部会比两边更快地停止伸长，从而在形状上更像一个柱形。

　　在雪花的一生中，雪晶体可能遇到许多温度更高或更低的空气团，形成独特而又复杂的生长史。这使得雪花不尽相同。雪花的每一个臂状物看起来都十分相像。但晶体本身却是各式各样的。

　　利用冷却槽，Libbrecht发现了如何制造各种形状的雪晶体，碟状、柱状、针状的等等。Libbrecht还改进了他的技术，使得晶体之间更加相像。然而，他仍然无法制造两片完全相同的雪花。湿度与温度的细微差别就会改变晶体的形成过程。