单项选择题

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

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单项选择题

How did scientists discover the source of lead pollution in Green land

A．By analyzing the data published in journals like Nature and Ambio.
B．By observing the lead accumulation in different parts of the arctic area.
C．By studying the chemical elements of soil and snow in North eastern America.
D．By comparing the chemical compositions of leaded gasoline used in various countries.

单项选择题

What is the author's main point in the first paragraph

A．The penny press was modeled on earlier papers.
B．The press in the nineteenth century reached only a small proportion of the population,
C．The penny press became an important way of disseminating information in the first half of the nineteenth century.
D．The penny press focused mainly on analysis of polities.