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 was discouraged B was enforced by law C was prohibited by law D was introduced

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

A forests get rid of lead pollution faster than expected B lead accumulations in forests are more difficult to deal with C lead deposits are widely distributed in the forests of the US D the upper layers of soil in forests are easily polluted by lead emissions

A are puzzled by the mystery of forest pollution B feel relieved by the use of unleaded gasoline C still consider lead pollution a problem D lack sufficient means to combat lead pollution

A The reasons behind the plunge of oil prices. B Possible ways to stimulate the global economy. C The impact of cheap oil on global economic growth. D The effect of falling oil prices on consumer spending.

A Manufacturers can produce consumer goods at a much lower cost. B Lower oil prices have always given a big boost to the global economy C Oil prices may rise or fall but economic laws are not subject to change. D Consumers will spend their savings from cheap oil on other commodities

A They suspend import of necessities from overseas. B They reduce production drastically to boost oil prices. C They use their money reserves to back up consumption. D They try to stop their economy from going into free-fall

A It is one that has seen no parallel in economic history. B Its negative effects more than cancel out its positive effects. C It still has a chance to give rise to a boom in the global economy. D Its effects on the global economy go against existing economic laws.

A People are not spending all the money they save on gas. B The global economy is likely to undergo another recession. C Oil importers account for a larger portion of the global economy. D People over the world are afraid of a further plunge in oil prices