Text 2

　　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 photo chemically 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。

　　26. 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。

　　27. 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 photo chemically 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。

　　28. 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。

　　29. 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。

　　30. 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。

　　Text 3

　　The use of heat pumps has been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as two units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation。

　　Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters a compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body of air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from the air to the refrigerant, reducing the temperature of this second body of air. Of the two heat exchangers, one is located inside, and the other one outside the house, so each is in contact with a different body of air: room air and outside air, respectively。

　　The flow direction of refrigerant through a heat pump is controlled by valves. When the refrigerant flow is reversed, the heat exchangers switch function. This flow-reversal capability allows heat pumps either to heat or cool room air。

　　Now, if under certain conditions a heat pump puts out more thermal energy than it consumes in electrical energy, has the law of energy conservation been challenged? No, not even remotely: the additional input of thermal energy into the circulating refrigerant via the evaporator accounts for the difference in the energy equation。

　　Unfortunately there is one real problem. The heating capacity of a heat pump decreases as the outdoor temperature falls. The drop in capacity is caused by the lessening amount of refrigerant mass moved through the compressor at one time. The heating capacity is proportional to this mass flow rate: the less the mass of refrigerant being compressed, the less the thermal load it can transfer through the heat-pump cycle. The volume flow rate of refrigerant vapor through the single-speed rotary compressor used in heat pumps is approximately constant. But cold refrigerant vapor entering a compressor is at lower pressure than warmer vapor. Therefore, the mass of cold refrigerant — and thus the thermal energy it carries — is less than if the refrigerant vapor were warmer before compression。

　　Here, then, lies a genuine drawback of heat pumps: in extremely cold climates — where the most heat is needed — heat pumps are least able to supply enough heat.31. The primary purpose of the text is to [A] explain the differences in the working of a heat pump when the outdoor temperature changes. [B] contrast the heating and the cooling modes of heat pumps. [C] describe heat pumps, their use, and factors affecting their use. [D] advocate the more widespread use of heat pumps.32. The author resolves the question of whether heat pumps run counter to the principle of energy conservation by [A] carefully qualifying the meaning of that principle. [B] pointing out a factual effort in the statement that gives rise to this question. [C] supplying additional relevant facts. [D] denying the relevance of that principle to heat pumps.33. It can be inferred from the text that, in the course of a heating season, the heating capacity of a heat pump is greatest when [A] heating is least essential. [B] electricity rates are lowest. [C] its compressor runs the fastest. [D] outdoor temperatures hold steady.34. If the author’s assessment of the use of heat pumps (lines 1-4) is correct, which of the following best expresses the lesson that advertisers should learn from this case? [A] Do not make exaggerated claims about the products you are trying to promote. [B] Focus your advertising campaign on vague analogies and veiled implications instead of on facts. [C] Do not use facts in your advertising that will strain the prospective client’s ability to believe. [D] Do not assume in your advertising that the prospective clients know even the most elementary scientific principles.35. The text suggests that heat pumps would be used more widely if [A] they could also be used as air conditioners. [B] they could be moved around to supply heat where it is most needed. [C] their heat output could be thermostatically controlled. [D] people appreciated the role of the evaporator in the energy equation。