请阅读下列段落,并分析段落是按照哪种结构模式展开比较的。 The public transportation system in Paris consists of subways and buses. Paris has one of the best subway systems in the world. The subway, or metro, spans the entire city of Paris, linking one end of the city with another. Most people in Paris travel by metro because it is fast, economical and convenient. The bus system in Paris is also quite good. For Parisians, having a car is a luxury, not a necessity. One the other hand, public transportation in American cities leaves a lot to be desired. Subways, in cities that have them, can be expensive and inconvenient—inconvenient because only very small portion of a city are served. The bus remains the only true means of public transport in most cities, but one finds poor connections, indirect route, and high prices. For sanity’s sake, a car in the United States is not a luxury. (Neufeld, 1987, p.67)