41.Some even argue plausibly that this weakness may be irremediable：in any society that, like a capitalist society, seeks to become ever wealthier in material terms  disproportionate rewards are bound to flow to the people who are instrumental in producing the increase in its wealth.

42.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.

43.These dramatic elements, along with an intensely social or political purpose and the use of a mixture of Spanish, English, and Mexican American dialects in the dialogues, which    realistically capture the flavor of Mexican American conversation, are still characteristic both of the acto and of most other forms of Mexican American theater today.

44.The improvised comic satire of the actos is often attributed to Valdez" study of the Italian commedia dell" arte of the sixteenth century, although some critics see it as a direct reflection of the comic and improvisational qualities of the more contemporary and local carpas of Mexican theater.

45.The Italian influence is likely, whatever Valdez immediate source: the Mexican carpas themselves are said to have originated from the theater pieces of a sixteenth-century Spanish writer inspired by encounters with Italian commedia dell"arte troupes on tour in Spain.

46.But the recent discovery of detailed similarities in the skeletal structure of the flippers in all three groups undermines the attempt to explain away superficial resemblance as due to convergent evolution—the independent development of similarities between unrelated groups in response to similar environmental pressures.

47.In humans excessive intake ( for adults, over 4 milligrams per day) over many years can lead to skeletal fluorosis, a well-defined skeletal disorder, and in some plant species, fluoride is more toxic than ozone, sulfur dioxide, or pesticides.

48.And while fluoride intake from water and air can be evaluated relatively easily, it is much harder to estimate how much a given population ingests from foodstuffs because of the wide variations in individual eating habits and in fluoride concentrations in foodstuffs.

41.一些人甚至很有道理地指出，这个弱点可能是无法补救的：在任何类似于资本主义的社会，它始终追求越来越富有，在物质方面，不成比例的报酬肯定会流到那些人中，这些人对增加社会财富有帮助。

42.人们逐渐认识到，唯一有效的方法来进一步减少车辆尾气的排放量——除了大规模减少私人汽车——替换传统的柴油和汽油，用燃烧得更加清洁的燃料，比如说压缩天然气、液化石油气、乙醇、或者甲醇。

43.这些戏剧因素，连同(并列关系)一种强烈的社会或者政治目的，以及对话中西班牙语、英语、和美籍墨西哥人方言的混合使用，这种混合使用真实地捕捉住到美籍墨西哥人的对话韵味（特点），仍然是特征，acto戏剧和现在大多数其它形式的美国墨西哥戏剧的特征。

44.Actos戏剧的即兴的喜剧讽刺，经常被归功于Valdez对16世纪意大利c.d.a.（即兴喜剧）的研究，尽管有些评论家把它看作是直接反映，对于同时代的地方性的墨西哥carpas戏剧中喜剧和即兴特点的反映（影响）。

45.意大利的影响是可能的，不管Valdez的直接来源是什么：墨西哥carpas戏剧据说本身就来源于16世纪西班牙作家的戏剧作品，而这些西班牙作家受到启发，是因为遇到了（观看）意大利c.d.a. 剧团在西班牙的巡回演出。

46.但是，最近的发现，这三种动物的鳍足的骨骼结构都有详细的类似之处，这个发现削弱了下文的企图，即把表面上的类似解释为趋同进化的结果——是指类似结构的独立发展，在不相关的种群之间，对于类似的环境压力的反应。

47.人类过量的摄入（成人每天超过4毫克）多年以后会导致骨骼氟中毒，一种容易识别的骨骼混乱（病症），而且在某些植物中，氟化物的毒性要比臭氧、二氧化硫或者杀虫剂都大。

48.而且，虽然来自于水和空气中的氟化物摄入量相对容易测量，但是却难以测量出特定的人口从食物中摄入的氟化物含量，因为有很大的区别存在于个人的饮食习惯和不同食物的氟含量当中。