As concerns over man's impact on the global environment increase, many interesting innovations are being considered. For example, "green roofs" - plant-filled roof top gardens - are one substantial way to confront the country's ecological problems, and there seems to be very little in the way of a downside. For one thing, a green roof acts as a sponge for rainwater, absorbing the majority of water from a typical rainstorm. Only three to five inches of soil for a green roof is sufficient for this to occur, which keeps the weight of the roof to a minimum. Because the plantings on the roof absorb the rainwater, drainage and sewage systems have a decreased volume of water pumping through them, keeping these systems from becoming over-stressed. And while, the soil and plants are absorbing rainwater, they are also taking in pollutants for their own nourishment by storing carbon and then emitting necessary oxygen back into the atmosphere.

单选题 The second and third sentences are characterized, respectively, by

A. warning and justification
B. generalization and specification
C. invocation and definition
D. authority and reverence
E. confession and resolution

【正确答案】 B

【答案解析】The passage begins with an assertion that green roofs are a viable solution to the country's ecological problems. It then continues with specific ways by which green roofs would help.

单选题 The author's main point in the passage is that

A. green roofs are expensive to install and maintain
B. green roofs are both innovative and eco-friendly
C. global warming concerns have led to many new inventions
D. plant-filled roof gardens emit oxygen into the atmosphere
E. green roofs are the definitive cure for global warming

【正确答案】 B

【答案解析】According to the passage, green roofs are an example of an interesting innovation that will help with our ecological problems. Therefore, choice B is the best answer. The remaining choices are either too specific or too broad.

单选题 The author references the absorption capabilities of green roofs primarily in order to illustrate

A. a preoccupation with style over design practicality
B. the inefficiencies of installing plantings to a building's roof
C. how green roofs lead to more efficient and less-stressed home systems
D. the increased public interest in environmental friendliness in the construction industry
E. how global warming has accelerated society's interest in environmentally friendly structures

【正确答案】 C

【答案解析】The passage focuses on specific examples of how the green roofs would work. The other answer choices are outside the scope of the passage.

单选题 The Homestead Act of 1862 has been called one of the most important pieces of legislation in the history of the United States. Signed into law by Abraham Lincoln, this Act turned over vast amounts of the public domain to private citizens. 270 million acres, or 10% of the area of the United States was claimed and settled under this act. The Act provided that any head of a family who was a citizen, or declared his intention of becoming a citizen, could claim 160 acres of land. The claimants needed to pay a small registration fee and reside on the land for five years. Claimants were also required to build a home and grow crops on the land. If after five years, the original settler were still on the land, it would become his property, free and clear. Which of the following, if true, would most undermine the validity of the author's statements about the significance of the Homestead Act?

A. Most settlers had moved on from their claim sites before the end of five years.
B. Most settlers chose to grow non-food crops.
C. Some congressmen thought there should be no registration fee for settlers.
D. Some non-citizen claimants were unable to become citizens.
E. Some of the land was unsuited to growing wheat.

【正确答案】 A

【答案解析】According to the passage, the Homestead Act of 1862 is one of the most important pieces of legislation in the history of the United States. However, claimants were supposed to reside on their property for five years in order to own it. If the majority of claimants left their land before the end of the five-year period, that would call into question the effectiveness of the Act.