生态系统（ecosystem)

A.译码

B.经济学

C.生态系统

D.礼仪

根据是否直接满足服务消费者的需求，可以将服务生态系统(Services ecosystem)中的服务分为垂直(Vertical)服务和水平(Horizontal)服务。因此，在进行服务系统构建的时候，可以事先将服务分划为这两种类型，并按照其特点，应用不同的设计原则，分别进行分析和设计。()

参考答案：错误

生态系统

Passage Three Questions 21 to 25 are based on the following passage.

Lead deposits, which accumulated in soil and snow during the 1960's and 70's, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation world-wide has decreased significantly.

A study published recently in the journal Nature shows that air-borne leaded gas emissions

from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic(北极的 ) snow were declining.

In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate (分区) the lead sources. The dominant lead

ratio found in Greenland snow matched that found in gasoline from the United States.

In a study published in the journal Ambio, scientists found that lead levels in soil in the North-eastern United States had decreased markedly since the introduction of unleaded gasoline.Many scientists had believed that the lead would stay in soil and snow for a longer period.

The authors of the Ambio study examined samples of the upper layers of soil taken from thesame sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990.

The forest environment processed and redistributed the lead faster than the scientists had expected.

Scientists say both studies demonstrate that certain parts of the ecosystem (生态系统 ) re-spond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.

21. The study published in the journal Nature indicates that

A．the Clean Air Act has not produced the desired results

B．lead deposits in arctic snow are on the increase

C．lead will stay in soil and snow longer than expected

D．the US is the major source of lead pollution in arctic snow

A.海岸生态系统

B.淡水生态系统

C.森林生态系统

D.航天器生态系统

A.人工生态系统

B.自然生态系统

C.半自然生态系统

D.封闭式生态系统

A.海岸生态系统

B.近海海洋生态系统

C.部分陆地生态系统

D.部分陆地生态系统

A.海洋生态系统

B.湿地生态系统

C.草原生态系统

D.森林生态系统