目前汽车上使用的铜及其合金主要有工业纯铜、黄铜和青铜。据统计,一辆载货汽车需要20kg左右的铜。
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Now, the VOA Special English program, Words and Their Stories.Every people has its ___(1)____ way of saying things, its own special expressions. Many everyday American expressions are based on __(2)___.Red is a hot color. Americans often use it to express _(3)__. They may say they are red hot about something _(4)__. When they are red hot they are very angry about something. The small hot tasting peppers found in many Mexican foods are called red hots for their color and their fiery taste. Fast loud music is popular with many people. They may say the music is red hot, especially the kind called Dixieland jazz.Pink is a lighter kind of red. People sometimes say they are in the pink when they are in good _(5)_. The expression was first used inAmericaat the beginning of the twentieth century. It probably comes from the fact that many babies are born with a nice pink color that shows that they are in good health._(6)_ is a cool color. The traditional blues music in theUnited Statesis the opposite of red hot music. Blues is slow, sad and soulful. Duke Ellington and his orchestra recorded a famous song – Mood Indigo – about the deep blue color, indigo. In the words of the song: "You ain't been blue till you've had that Mood Indigo." Someone who is blue is very _(7)_.The color green is natural for trees and grass. But it is an _(8)_ color for humans. A person who has a sick feeling stomach may say she feels a little green. A passenger on a boat who is feeling very sick from high waves may look very green.Sometimes a person may be upset because he does not have something as nice as a friend has, like a fast new car. That person may say he is green with _(9)_. Some people are green with envy because a friend has more dollars or greenbacks. Dollars are called greenbacks because that is the color of the back side of the paper money.The color black is used often in expressions. People describe a day in which everything goes wrong as a black day. The date of a major _(10)_ is remembered as a black day. A blacklist is illegal now. But at one time, some businesses refused to employ people who were on a blacklist for belonging to unpopular organizations.In some cases, colors describe a situation. A brown out is an expression for a _(11)_ in electric power. Brown outs happen when there is too much _(12)_for electricity. The electric system is unable to offer all the power needed in an area. _(13)_ outs are common during World War two. Officials would order all lights in a city turned off to make it difficult for enemy planes to find a target in the dark of night.I'm Warren Scheer. Listen again next week for another Words and Their Stories program in Special English on the Voice of America.
半径为R的肥皂泡内气体压强等于( )。已知外界大气压为P0,肥皂液的表面张力系数为α。
A. P0+4α/R
B. P0+2α/R
C. P0-4α/R
D. P0-2α/R
有一直径为4 mm的水银滴,温度在20℃时的表面张力系数为470×10-3 N·m-1,水银滴的附加压强等于( )Pa。
在面向过程方式中,开发者关心的是完成任务所经历的(),将这些步骤定义成函数后,依次调用来完成任务。在面向对象方式中,开发者更关心任务中涉及到的(),即洗衣机对象和衣服对象。