Questions are based on the following passage. Americans seem to be cooling toward global warming. Just 57 percent think there is sol-id evidence the world is getting warmer， down 20 points in just three years， a new poll says. And the share of people who believe pollution caused by humans is causing temperatures torise has also taken a dip， even as the US and world forums gear up for （准备） possible ac-tion against climate change. In a poll of 1，500 s released by the Pew Research Centre for the People & the Press，the number of people saying there is strong scientific evidence that the Earth has gottenwarmer over the past few decades is down from 71 percent in April of last year and from 77percent when Pew started asking the question in 2006. The number of people who see thesituation as a serious problem also has declined. The steepest drop has occurred during the past year， as Congress and the Obama admin-istration have taken steps to control heat-trapping emissions for the first time and interna-tional negotiations for a new treaty to slow global warming have been under way. At thesame time， there has been mounting scientific evidence of climate change —— from meltingice caps to the world's oceans hitting the highest monthly recorded temperatures this summer. The poll was released a day after 18 scientific organisations wrote Congress to reaf-firm the consensus behind global warming. A federal government report recently found thatglobal warming is upsetting the Arctic's thermostat （恒温器）. Only about a third， or 36 percent of the respondents， feel that human activities —— suchas pollution from power plants， factories and automobiles —— are behind a temperature in-crease. That's down from 47 percent from 2006 through last year's poll. 'The priority that people give to pollution and environmental concerns and a whole hostof other issues is down because of the economy and because of the focus on other things，'suggested Andrew Kohut， the director of the research center， which conducted the poll fromSept.30 to Oct.4. 'When the focus is on other things， people forget and see these issues asless grave，' Andrew Weaver said， a professor of climate ysis at the University of Victo-ria in British Columbia， 'and politics could be drowning out scientific awareness.' The phrase 'taken a dip' （Line 4， Para.1） is the closest in meaning to __________. 查看材料