Alternative Energy Sources (可替代资源) When considering alternative energy sources to replace fossil fuels, it should be pointed out that our present technology is dependent on fossil-based energy in two main forms:electricity produced by burning coal, and portable chemical fuels such as petroleum or natural gas．At present not all countries are totally dependent on coal for electricity generation．For instance, nuclear power provided about 48% of the total energy requirements of Finland, France and Sweden in 1996．To a lesser extent, hydroelectric power (水力发电)is also providing electricity to many areas throughout the world．Despite their environmental problems, these alternatives are likely to supply our electricity requirements for at least the first ten years of the new century．However, many scientists are convinced that other less controversial alternatives such as solar and wind power, which convert heat or me- chanical energy directly into electricity, will provide a 'clean' energy for future generations early in the new century. In most industrialized nations, electricity supplies only a portion of the country's total energy needs, typically about 16%～25%．By far the largest share of a nation's total energy consumption is derived from chemical fuels which are either used for space heating or converted directly into mechanical energy in, for instance, an automobile engine．The great advantage of chemical fuels is their ease of transportation, storage'and utility in even the remotest areas．By contrast, electricity must be constantly generated since it is con sumed essentially the instant it is produced．It is therefore not surprising that recent scientific research has centered on developing a portable chemical fuel to replace fossil fuels. In addition to economic and environmental considerations, an alternative synthetic chemical fuel should, ideally, be produced from accessible raw materials that are not derived from fossil fuels．Thus, coal liquefaction (液化) cannot be considered as a satisfactory long-term solution．The production of biologicallyderived chemical fuels such as alcohol, produced from the ferment (发酵) of farm crops or from waste products; has also generated a lot of scientific and public interest．However, while these.biological fuels are less polluting than fossil fuels, they are still carbon-based molecules which, during the process of burning are less polluting than fossil fuels, send carbon dioxide (二氧化碳) and other pollutants (污染物) into the environment．Clearly, the only ideal long-term replacement for fuels such as petroleum is one that contains no carbon．Obviously, hydrogen meets this requirement. 第 36 题 The phrase 'these alternatives' (in Line 8 of Paragraph 1) refers to____.