27. The passage provides information on each of the following EXCEPT

A. when the pull theory originated
B. the amount of water a tall tree can transport
C. the significance of water's tensile strength in the pull theory
D. the role of the sun in the pull theory
E. the mechanism underlying water's tensile strength

属于传统上GRE阅读中比较难细节题，无法从题干本身获得定位主题词的信息。A项文中对应时间1800，B项所提最小单位可能是水分子。C项提到的tensile strength为理论涉及的基础性原理，26题已经有所涉及。D项对应文章末句。而E选项对文中信息做了推广延伸。在tensile strength更底层的具体原理机理文中没有进一步解释。

Producing and using biodiesel, a fuel derived from cultivated rapeseed, causes 35 percent less air pollution per gallon than does producing and using regular diesel fuel. The government plans to reduce diesel-related air pollution over the next decade by 25 percent, so replacing regular diesel with biodiesel would seem to be the obvious solution. Unfortunately, the greatest possible production of biodiesel would amount to only one percent of all diesel fuel to be produced during the next 15 years.

28. The passage is structured to lead to which of the following as a conclusion?

A. The use of biodiesel will increase by less than one percent over the next 15 years.
B. During the next 15 years, the production of biodiesel will be increased as fast as it is possible to increase it.
C. During the next 15 years, it will be impossible, just by switching to biodiesel, to meet the government's stated goal with respect to reducing air pollution.
D. Fifteen years from now, the air pollution caused by the production and use of one gallon of regular diesel fuel will be far less than it currently is.
E. There will be no significant year-to-year increase in the amount of regular diesel fuel used during the next 15 years.

全文给出了很多细节性的数字，而解题需要对相关数字做出简单推算。可以设现在每加伦传统diesel油的污染x，现在一年需要消耗的油量y加伦。简单估算后，产量严重限制了最后biodiesel最后对减少污染的实际作用，所以正确答案为C。A选项混淆了产量和使用情况；B选项与原文末句叙述不符；D选项比较的是一加仑现在使用的diesel油与15年后污染情况；E选项比较具有迷惑性，但是核心主体为diesel，而不是文中的biodiesel。