单选题
Scientists measured the impact that people have on the environment using a term called carbon "footprint". That footprint reflects the amount of carbon dioxide that is emitted (排放) into the atmosphere as a result of someone"s daily activities. Carbon footprints tend to be low for city dwellers(城镇居民). Living in a suburb outside a city, however, can turn that footprint into a bootprint.
Energy researchers Christopher Jones and Daniel Kammen calculated carbon footprints for people in every zip code across the United States. People living in city centers had small footprints, the researchers found. "It is much easier to have a low carbon impact if your home is close to where you work, shop and play," explains Jones. Living within walking, or biking distance cuts back on the amount of carbon dioxide associated with moving people by cars. And cities with expensive bus and subway networks allow people to travel great distances while keeping releases of climate-altering greenhouse gases low.
Not everyone can afford to live in the city, however. And not everyone wants to. Rings of suburbs have popped up around major cities across the world. Suburbs offer more space, allowing people to build larger homes. Suburbs may offer better schools for a family"s kids. But those homes are typically well beyond walking distance from where their owners work, play or learn. So people who live in suburbs often drive long distances.
The new findings are an important contribution to climate research, says Matthew Kahn, an environmental economist at the University of California, who was not involved with the study. Kahn would like to see the analysis applied to other parts of the world—Europe, India and China, for instance. That would give scientists a better feel for how culture might mix with location to influence our carbon footprints.
单选题
"Footprint" refers to the amount of carbon dioxide released by ______.
【正确答案】
A
【答案解析】[解析] 根据文章第一段第二句“That footprint reflects the amount of carbon dioxide...of someone"s daily activities. ”可知，footprint指一个人在日常生活中排放到大气中的二氧化碳的量。故选A。
单选题
What is the new finding concerning the footprints of people living in cities and those living in suburbs?
【正确答案】
D
【答案解析】[解析] 根据文章第一段最后两句“Carbon footprints tend to be low for city dwellers. Living in a suburb outside a city, however, can turn that footprint into a bootprint. ”可知，城镇居民的碳排放量很低，而居住在城郊会增加二氧化碳的排放。故选D。
单选题
What is the key factor mentioned to explain the new findings?
【正确答案】
B
【答案解析】[解析] 根据文章第二段第四句“Living within walking, or biking distance cuts back on the amount of carbon dioxide associated with moving people by cars. ”可推知，解释新发现的关键因素是开车的距离。故选B。
单选题
What does Matthew Kahn think of the new findings?
【正确答案】
A
【答案解析】[解析] 根据文章最后一段第一句“The new findings are an important contribution to climate research...”可知，马修对该发现给予了较高的评价。故选A。
单选题
What is the purpose of the author in writing the passage?