单项选择题

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.
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

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单项选择题

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

单项选择题

If A is the point (-4, 1) and B is the point (2, 1), what is the area of the circle which has AB as a diameter（）

A. 3π
B. 6π
C. 9π
D. 12π
E. 36π