SAMPLE 18

　　[環(huán)境科學(xué)類]

　　Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such vehicles has been steadily increasing. Consequently, more than 100 cities in the United States still have levels of carbon monoxide, particulate matter, and ozone (generated by photochemical reactions with hydrocarbons from vehicle exhaust) that exceed legally established limits. There is a growing realization that the only effective way to achieve further reductions in vehicle emissions — short of a massive shift away from the private automobile — is to replace conventional diesel fuel and gasoline with cleaner-burning fuels such as compressed natural gas, liquefied petroleum gas, ethanol, or methanol.

　　All of these alternatives are carbon-based fuels whose molecules are smaller and simpler than those of gasoline. These molecules burn more cleanly than gasoline, in part because they have fewer, if any, carbon-carbon bonds and the hydrocarbons they do emit are less likely to generate ozone. The combustion of larger molecules, which have multiple carbon-carbon bonds involves a more complex series of reactions. These reactions increase the probability of incomplete combustion and are more likely to release uncombusted and photochemically active hydrocarbon compounds into the atmosphere. On the other hand, alternative fuels do have drawbacks. Compressed natural gas would require that vehicles have set of heavy fuel tanks — a serious liability in terms of performance and fuel efficiency — and liquefied petroleum gas faces fundamental limits on supply.

　　Ethanol and methanol, on the other hand, have important advantages over other carbon-based alternative fuels: they have higher energy content per volume and would require minimal changes in the existing network for distributing motor fuel. Ethanol is commonly used as a gasoline supplement, but it is currently about twice as expensive as methanol, the low cost of which is one of its attractive features. Methanol’s most attractive feature, however, is that it can reduce by about 90 percent the vehicle emissions that form ozone, the most serious urban air pollutant.

　　Like any alternative fuel, methanol has its critics. Yet much of the criticism is based on the use of “gasoline clone” vehicles that do not incorporate even the simplest design improvements that are made possible with the use of methanol. It is true, for example, that a given volume of methanol provides only about one-half of the energy that gasoline and diesel fuel do; other things being equal, the fuel tank would have to be somewhat larger and heavier. However, since methanol-fueled vehicles could be designed to be much more efficient than “gasoline clone” vehicles fueled with methanol they would need comparatively less fuel. Vehicles incorporating only the simplest of the engine improvements that methanol makes feasible would still contribute to an immediate lessening of urban air pollution.

　　1. The author of the text is primarily concerned with

　　[A] countering a flawed argument that dismisses a possible solution to a problem.

　　[B] reconciling contradictory points of view about the nature of a problem.

　　[C] identifying the strengths of possible solutions to a problem.

　　[D] discussing a problem and arguing in favor of one solution to it.

　　2. According to the text, incomplete combustion is more likely to occur with gasoline than with an alternative fuel because

　　[A] the combustion of gasoline releases photochemically active hydrocarbons.

　　[B] the combustion of gasoline embraces an intricate set of reactions.

　　[C] gasoline molecules have a simple molecular structure.

　　[D] gasoline is composed of small molecules.

　　3. The text suggests which of the following about air pollution?

　　[A] Further attempts to reduce emissions from gasoline-fueled vehicles will not help lower urban air-pollution levels.

　　[B] Attempts to reduce the pollutants that an individual gasoline-fueled vehicle emits have been largely unsuccessful.

　　[C] Few serious attempts have been made to reduce the amount of pollutants emitted by gasoline-fueled vehicles.

　　[D] Pollutants emitted by gasoline-fueled vehicles are not the most critical source of urban air pollution.

　　4. Which of the following most closely parallels the situation described in the first sentence of the text?

　　[A] Although a town reduces its public services in order to avoid a tax increase, the town’s tax rate exceeds that of other towns in the surrounding area.

　　[B] Although a state passes strict laws to limit the type of toxic material that can be disposed of in public landfills, illegal dumping continues to increase.

　　[C] Although a town’s citizens reduce their individual use of water, the town’s water supplies continue to dwindle because of a steady increase in the total populating of the town.

　　[D] Although a country attempts to increase the sale of domestic goods by adding a tax to the price of imported goods, the sale of imported goods within the country continues to increase.

　　5. It can be inferred that the author of the text most likely regards the criticism of methanol as

　　[A] flawed because of the assumptions on which it is based.

　　[B] inapplicable because of an inconsistency in the critics’ arguments.

　　[C] misguided because of its exclusively technological focus.

　　[D] inaccurate because it ignores consumers’ concerns.
　　[答案與考點解析]

　　1. 【答案】C

　　【考點解析】這是一道中心主旨題。本文的中心主旨句是首段的尾句。通過對首段尾句以及其它段落主題句的閱讀和理解，可以推導(dǎo)出本題的正確選項是C�？忌�在破解此類題型時一定要首先抓住原文的中心主旨句以及各段的主題句。

　　2. 【答案】B

　　【考點解析】本題是一道指代詞題型。根據(jù)題干中的“incomplete combustion”可將本題的答案信息來源迅速確定在第二段的第四句，該句中的指代詞“these”暗示本題的具體答案信息來源應(yīng)該在第二段的第三句。通過閱讀和理解第二段的第三句可推導(dǎo)出本題的正確選項是B�？忌�在解題時對指代詞一定要認(rèn)真理解。

　　3. 【答案】A

　　【考點解析】本題是一道審題定位題型。通過題干中的“air pollution”可將本題的答案信息來源迅速確定在第一段，因為第一段首句中含有“noxious pollutants”，都在談污染的問題。通過閱讀和理解第一段，尤其是第一段尾句即全文的中心主旨句，可推導(dǎo)出本題的正確選項是A。這是一道比較難的題�？忌�在解題時一定要具備審題定位能力，還要具備歸納和推導(dǎo)能力。

　　4. 【答案】C

　　【考點解析】這是一道類比題型，因為本題題干中含有“parallels”(與……相當(dāng)，與……一樣)一詞。本題題干已將類比的參照對象確定在第一段的首句。通過仔細閱讀和理解第一段的首句，可推導(dǎo)出本題的正確選項是C，因為該選項涉及的增減關(guān)系的前提條件和原文一脈相承�？忌�在破解這種題型時應(yīng)對原文所表達的內(nèi)容與關(guān)系有明確的認(rèn)識和把握，不可以無根據(jù)地推導(dǎo)。

　　5. 【答案】A

　　【考點解析】這是一道細節(jié)推導(dǎo)題型。本題題干中的“the criticism of methanol”把本題的答案信息來源確定在第四段的第一、二句。通過閱讀和理解這兩句話，尤其是第二句話，就可推導(dǎo)出本題的正確選項A�？忌�在破解本題時一定要注意第二句話的第一個詞“Yet”在語意上所起的作用�？忌�在解題時一定要重視啟承轉(zhuǎn)合詞的出現(xiàn)和功能。

　　[參考譯文]

　　近年來，盡管單個機動車輛排放的有毒污染物已大幅減少，但這些機動車輛的數(shù)量一直在持續(xù)增長，結(jié)果是，在美國有100多個城市的大氣中一氧化碳、灰塵和臭氧(由車輛尾氣中的碳氫化合物經(jīng)光化反應(yīng)產(chǎn)生)的含量已超出了法定的限度。人們愈來愈認(rèn)識到，實現(xiàn)車輛廢氣進一步減少而又不必大規(guī)模減少私家轎車的唯一有效途徑是用清潔燃料來代替?zhèn)鹘y(tǒng)的柴油和汽油燃料。這些清潔燃料包括壓縮天然氣、液化石油氣、乙醇和甲醇。

　　所有這些替代產(chǎn)品都是碳基燃料，不過它們的分子要比汽油的分子小且簡單。它們可以比汽油燃燒得更徹底，部分原因在于，即使它們含有碳—碳化學(xué)鍵，含量也較少，而且它們釋放的碳氫化合物也不大可能產(chǎn)生臭氧。那些具有多重碳——碳化學(xué)鍵的大分子在燃燒時包含了一系列復(fù)雜的反應(yīng)。這些反應(yīng)增大了不完全燃燒的可能，并且更容易釋放未燃燒的碳氫化合物，而這些化合物又對光化學(xué)反應(yīng)很活躍。另一方面，這些替代燃料也有自己的缺點。壓縮天然氣可能需要車輛配備一個笨重的油箱，這對車輛性能和燃料效率又極為不利，并且液化石油氣還面臨著供應(yīng)上的根本限制。

　　從另一方面來看，甲醇和乙醇與其它的碳基替代燃料相比有重要的益處：它們具有單位體積更高的能量含量，而且對現(xiàn)存的燃料銷售網(wǎng)絡(luò)只需很小地改變。乙醇通常作為汽油的替代品，但目前它比甲醇要貴兩倍，因此甲醇的低廉價格便成為引人注目的特點。然而，甲醇最吸引人的特點還在于它可以減少90%形成臭氧的廢氣，而臭氧又是城市中最嚴(yán)重的污染物。

　　和其它的替代燃料一樣，甲醇也遭到了非難�？纱蠖鄶�(shù)批評都建立在使用“汽油系列”的車輛不進行最簡單的設(shè)計改進以可能使用甲醇燃料的基礎(chǔ)上。例如，事實上一定體積的甲醇和同體積的汽油和柴油相比，只能提供相當(dāng)于它們大約一半的能量。在其它因素相同的條件下，油箱可能要大一點和重一點，然而，由于甲醇燃料的車輛可以設(shè)計得比使用甲醇的“汽油系列”車輛還要高效，它們可能需要更少的燃料。同時，對發(fā)動機進行最簡單的改進便可使用甲醇的車輛，這將對城市大氣污染的迅速減輕做出貢獻。