20.Why do some Japanese parents send their
children to university-based kindergartens? They can ___.
A) do better in their future studies
B) accumulate more group experience there
C) be individually oriented when they
grow up
D) have better chances of getting a
first-rate education
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 worldwide has decreased significantly.
A study published recently
in the journal Nature shows that air-borne leaded gas emissions form 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(区分)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 Northeastern 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 the same sites of
20 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) respond rapidly to reductions in atmospheric pollution, but that
these findings should not be used as a license to pollute.