单选题In the metals industry, hydrogen is used to prevent metals from tarnishing while undergoing__________.

单选题(It is) believed that some dinosaurs were intelligent, (ability) to perform complex activities,and perhaps (even) capable of (social) behavior.

单选题(Hard. and resistant to corrosion, bronze (is traditionally) used in bell casting and is the material used (widely most) for metal (sculpture.. A. Hard B. is traditionally C. widely most D. sculpture

单选题Listening5"MusicAppreciationClass"

单选题Stone tools began to be replaced around 6,000 years ago by metal tools, who were used to build instruments and simple machines.

单选题Perhaps the most distinctive (features) of sharks and (undoubtedly) one of the most important (reasons) for their success is their well-developed (sensory) system.

单选题Which of the following questions does the passage primarily answer?

单选题Although the sensory receptors and brain pathways for taste and smell are independent, the two senses do interact. A great deal of what we consider taste is actually smell. If the sense of smell is obstructed, as by a head cold, the perception of taste is sharply reduced. 1. The word obstructed in the passage is closest in meaning to

单选题According to the passage, the maria differ from the terrace mainly in terms of

单选题Compared to the tail of electrically charged atoms, the tail of neutral dust particles is relatively

单选题Abigail Adams was prodigious letter writer, ______ many editions of her letters have been published. A. who B. and C. in addition to D. due to

单选题Fluorine is a greenish gas too active that even water and glass burn in it.

单选题The eighteenth century witnessed the emergence of North American ports, particular Boston, New York, and Philadelphia, as major commercial centers within the British empire.

单选题According to the passage, one advantage of sea island cotton was its

单选题Whatisthetalkmainlyabout?A.Thesatisfactory"buy-now,pay-later"creditsystem.B.Thewaysthecreditcompaniesusetoissuecreditcards.C.Theclassificationandadvantagesanddisadvantagesofcreditcards.D.Thedifferencebetweenstorecreditcardsandothercreditcards.

单选题High-speed photography has made------certain aspects of motion never before seen,

单选题1 In the early nineteenth century, most of the Europeans who immigrated to the United States were from northern and western European countries such as England, Germany, France, and Sweden. However, most of the fifteen million Europeans arriving between 1890 and 1914 came from southern and eastern Europe, with the largest numbers coming from Russia, Italy, Greece, Austria-Hungary, and Armenia. 2 A similar pattern occurred in Canada, where most immigrants were traditionally from England and the United States. After 1890, an increasing number came from eastern Europe, particularly Russia and Ukraine. Many of these headed for the Prairie Provinces. The Doukhobors, a pacifist sect from southern Russia, established communal settlements in Saskatchewan. Together with other immigrants, they arrived in such numbers that in the two decades between the completion of the main railroad network and the outbreak of war in 1914, the population of the prairies had increased from about 150,000 to 1.5 million.

单选题Air Pollution and Acid Rain The increasing variety and prevalence of pollution presents the world with many extremely daunting problems, air pollution in particular ranks among the most serious. In the following text, air pollution and acid rain caused by automobiles will be discussed. Certain solutions to the problem will be provided in the conclusion. It is widely known that cars are the main cause of air pollution in cities, accounting for 60% to 90% of all air pollution. This will get worse as the number of cars increases in urban areas. How do cars cause air pollution? First we must examine how a car works. There's a mixture of petrol in the car's internal combustion engine which create the force for the automobile to move. Unfortunately, in this process there are some poisonous chemicals which remain; these poisonous chemicals mainly come out of the car through the exhaust, it's not just what comes out of the car exhaust that is dangerous, the brake system also causes pollution. Brakes on cars release asbestos, it is a highly dangerous substance and it can kill humans. Also, the tires themselves give off small rubber particles which are not very healthy. Acid rain caused by air pollution has strongly influenced people's lives. It is almost impossible to describe the mathematical relationship between what goes up as pollutant emissions and what comes down as acid rain. However, we do know the primary source of acid rain is the pollution released by power plants. The pollutants combine with moisture in the atmosphere and then fall as an acid rain. Germans often call it royal water, because it can break down gold. The royal water falls in the form of rain or snow on the German Black Forest and attacks the soil. Microorganisms within the soil perish and metals harmful to trees like aluminum leak into the ground. At the same time, the acid rain attacks the trees' leaves and dissolves their waxy coating. The leaves then shrivel and die. About one in every ten trees in the Black Forest is a fir. 76% of all firs in the Black Forest are dying. 41% of all spruce are diseased, 43% of all pine are diseased, 26% of beech trees and 16% of all other trees are dying. Environmental groups like Green Peace campaign around Europe trying to stop the causes of acid rain. We need to find solutions to this problem. First, we should try and discourage the overuse of cars. We could do this by raising taxes on petrol or by making cars more expensive. Second, we can encourage alternative methods of transportation. For example, in Shanghai recently, a subway has been built underground, which takes some of the pressure off the roads. Some people would rather use the underground than drive their cars. Next, we could develop and use cleaner fuels instead of petrol. For example, we might use natural gas in the future or we might experiment with battery powered cars. Finally, the actual by-products of vehicle emissions must be managed.(A) [■] Scientists and engineers are now trying to use mechanical means for reducing the amount of chemicals that are emitted from cars' exhaust pipes.(B) [■] Germany is now leading the way in attacking this part of the problem.(C) [■] In order to clean up motor vehicle emissions, all new cars in Germany must now meet new emission standards and be fitted with a device called a catalytic converter.(D) [■] This is a device that is fixed over the exhaust and controls the carbon monoxide and other dangerous chemicals that cars give off. Like Germany, the United States also introduced strict clean air-controls on motor vehicle emissions in the mid-70s as part of their efforts to reduce acid rain. It's unlikely that any one of these solutions will work on its own. It will take a combination of all four of these solutions to help solve the air pollution problem.

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