依蜡皮膜结构分类，蜡可分为（）两大类。A、标准型蜡 B、抛光用蜡 C、乳化型蜡 D、抛光、

如图是一个电子门铃，当两个导线夹子相接触时，电子门铃有音

乐声，小明利用它检测以下物品是否导电，将下列物品分别接入两夹子之间，

能使门铃发出音乐声的

A．塑料尺

B．铅笔芯

C．橡皮

D．胸卡

By the mid-nineteenth century, the term "icebox" had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. The ice trade grew with the growth of cities. Ice was used in hotels, taverns(酒馆), and hospitals, and by some forward-looking city dealers in fresh meat, fresh fish, and butter. After the Civil War (1861-1865), as ice was used to refrigerate freight cars, it also came into household use. Even before 1880, half of the ice sold in New York, Philadelphia, and Baltimore, and one-third of that sold in Boston and Chicago, went to families for their own use. This had become possible because a new household convenience, the icebox, a precursor (前身) of the modern fridge, had been invented.

　　Making an efficient icebox as not as easy as we might now suppose. In the early nineteenth century, the knowledge of the physics of heat, which was essential to a science of refrigeration, was rudimentary(未发展的). The commonsense notion that the best icebox was one that prevented the ice from melting was of course mistaken, for it was the melting of the ice that performed the cooling. Nevertheless, early efforts to economize ice included wrapping up the ice in blankets, which kept the ice from doing its job. Not until near the end of the nineteenth century did inventors achieve the delicate balance of insulation(绝缘) and circulation needed for an efficient icebox.

　　But as early as 1803, and ingenious Maryland farmer, Thomas Moore, had been on the right track. He owned a farm about twenty miles outside the city of Washington, for which the village of Georgetown was the market center. When he used an icebox of his own design to transport his butter to market, he found that customers would pass up the rapidly melting stuff in the tubs of his competitors to pay a premium price(高价) for his butter, still fresh and hard in neat, one-pound bricks. One advantage of his icebox, Moore explained, was that farmers would no longer have to travel to market at night in order to keep their produce cool.

小题1:Where was ice used after the Civil War?

A．In refrigerating freight cars and households.

B．In hotels, taverns and hospitals

C．In families of New York, Philadelphia, and Baltimore.

D．In fresh meat, fish and butter by city dealers.小题2:What was essential to to make an icebox efficient according to the passage?

A．Keeping the ice from melting

B．Knowledge of the physics of heat.

C．Balance of insulation and circulation

D．Making efforts to reduce the use of ice小题3:The second paragraph is mainly about_____

A．the deveopment of icebox

B．the theoretical foundation of icebox

C．the wrong ideas about icebox

D．the way of using icebox小题4: What can we infer from the text?

A．Thomas Moore is the inventor of modern fridge

B．The butter produced by Thomas Moored is better in quality than other famers’

C．Knowledge of the physics of heat plays an important part in inventing a good icebox

D．Before 1880, most of the sold ice was used for family use.小题5: Without an ice box, farmers had to go to the market at night ________.

A．to sell their produce at high price

B．to go home earlier

C．to keep their produce fresh

D．to win more customers than their competitors

用电阻式调速的车辆，要提高车速要使（）就可达到。

A、主回路总阻抗减少，电枢电压增大

B、主回路总阻抗增大，电枢电压减少

C、总阻抗等于电枢电压子表

D、主回路总阻抗减少，电枢电压减少

聚丙烯酰胺凝胶电泳分离蛋白质除一般电荷效应外，还具有（）

A.重力作用

B.分子筛作用

C.扩散作用

D.电渗作用

E.吸附作用

相对主叫信令来说，被叫信令包含有一个（）的过程，其他流程同主叫信令流程。