Overlooking the swollen banks of the Missouri River at Omaha's riverfront landing, one scientist has an important explanation for the past three months of flooding .While many consider the flood to be man-made, a result of water released by the US. Army Corps of Engineers upriver, his theory aims to look deeper into the root of the problem. "The Missouri River is flooding," said Dr. James Hansen, Director of NASA's Goddard Institute for Space Studies, during a visit to Omaha on Tuesday."We've had floods that usually only happen once in every hundred years a couple of times on the Missouri River recently. That's one of the expected consequences of the increasing level of atmospheric carbon dioxide." Hansen, who is considered to be one of the world's leading experts on global warming , said the Missouri River is an example of how global warming is affecting the earth ."Unless you do statistics ,and you see that the frequency of these events is changing , it's not so easy to see that changes are occurring , because the climate system has large inertia  ,"he said . Hansen explained, "The ocean is four kilometers deep, and the ice sheets are two or three kilometers thick , so they don't respond immediately as we begin to change the atmospheric composition .We've only experienced about half of the warming that will be caused by the gases already in the atmosphere .The full effect is going to be felt by our children and grandchildren .And if we continue to increase the amount of CO2, the effect will be even larger." Hansen drew a comparison, "If we spend more money than what we're taking in , we're leaving a debt for our children and grandchildren to deal with ."According to Hansen, the responsibility lies in effective policy making to fight against global warming .That includes a gradual reduction in carbon emissions .Hansen suggests that a rising price be placed on carbon emissions, which should be collected from the fossil fuel companies at the first sale . Without effective measures taken by the government, Hansen said the public could expect more of the recent extreme weather patterns,, including more severe droughts and floods in the decades ahead . Many people think the reason for the flooding of the Missouri River is   _  .
the army releasing water upriver the effects of global warming the increasing level of carbon dioxide the dam at Omaha's riverfront breaking
Question: Overlooking the swollen banks of the Missouri River at Omaha's riverfront landing, one scientist has an important explanation for the past three months of flooding .While many consider the flood to be man-made, a result of water released by the US. Army Corps of Engineers upriver, his theory aims to look deeper into the root of the problem. "The Missouri River is flooding," said Dr. James Hansen, Director of NASA's Goddard Institute for Space Studies, during a visit to Omaha on Tuesday."We've had floods that usually only happen once in every hundred years a couple of times on the Missouri River recently. That's one of the expected consequences of the increasing level of atmospheric carbon dioxide." Hansen, who is considered to be one of the world's leading experts on global warming , said the Missouri River is an example of how global warming is affecting the earth ."Unless you do statistics ,and you see that the frequency of these events is changing , it's not so easy to see that changes are occurring , because the climate system has large inertia  ,"he said . Hansen explained, "The ocean is four kilometers deep, and the ice sheets are two or three kilometers thick , so they don't respond immediately as we begin to change the atmospheric composition .We've only experienced about half of the warming that will be caused by the gases already in the atmosphere .The full effect is going to be felt by our children and grandchildren .And if we continue to increase the amount of CO2, the effect will be even larger." Hansen drew a comparison, "If we spend more money than what we're taking in , we're leaving a debt for our children and grandchildren to deal with ."According to Hansen, the responsibility lies in effective policy making to fight against global warming .That includes a gradual reduction in carbon emissions .Hansen suggests that a rising price be placed on carbon emissions, which should be collected from the fossil fuel companies at the first sale . Without effective measures taken by the government, Hansen said the public could expect more of the recent extreme weather patterns,, including more severe droughts and floods in the decades ahead . Many people think the reason for the flooding of the Missouri River is   _  .
A. the army releasing water upriver
B. the effects of global warming
C. the increasing level of carbon dioxide
D. the dam at Omaha's riverfront breaking
Answer: