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  3. In recent days, American Airlines has been forced to cancel more than 40 flights in Phoenix. The reason: With daytime highs hove

In recent days, American Airlines has been forced to cancel more than 40 flights in Phoenix. The reason: With daytime highs hove

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问题    In recent days, American Airlines has been forced to cancel more than 40 flights in Phoenix. The reason: With daytime highs hovering around 120 degrees, it was simply too hot for some smaller jets to take off. Hotter air is thinner air, which makes it more difficult—and sometimes impossible—for planes to generate enough lift. As the global climate changes, disruptions like these are likely to become more frequent, researchers say, potentially making air travel costlier and less predictable with a greater risk of injury to travelers from increased turbulence.
   "We tend to ignore the atmosphere and just think that the plane is flying through empty space, but of course, it’s not," said Paul D. Williams, a professor in the Department of Meteorology at the University of Reading in Britain. "Airplanes do not fly through a vacuum. The atmosphere is being modified by climate change." The problem in Phoenix primarily affected smaller jets operated by American’ s regional partner airlines.
   "When you get in excess of 118 or higher, you ’re not able to take off or land," said Ross Fein-stein, a spokesman for American Airlines, referring to the smaller aircraft. Bigger jets like Boeing 737s and Airbus A320s have higher operating thresholds (126 and 127 degrees, respectively), he said. But even though bigger planes weren ’t affected, he added, American decided to give passengers on any flight to or from Phoenix the option to change their trips.
   Overall, that means more than 350 flights were potentially affected by the hot weather in Phoenix. Robert Mann, the president of airline industry analysis firm R.W. Mann & Co., said that although airlines were working to become more efficient now, they were not doing much to prepare for the longer-term effects of climate change. "In a world where they’re focused on near-term issues, the glacial rate of environmental change is not within their fleet-planning horizon," he said.
   Researchers are just beginning to explore how climate change affects aviation and planes’ ability to fly. Because there is so little data available and so many factors at play—aircraft design, airport size and location, the weight of passengers and cargo, to name just a few—it can be hard to attribute any one service disruption to global warming.
   Depending on their locations, airports may experience the effects differently. La Guardia has a short runway relative to other major commercial airports, and on particularly hot days that can be a problem: Planes might not have enough distance to achieve the speed and lift needed to get airborne. "Typically in the hotter days of the summer, you may have to bump payload, which includes cargo and / or passengers," said David Wilhelm, a senior dispatch manager at Southwest Airlines. Reducing weight allows a plane to take off with less lift.
   As global temperatures continue to rise, some of the heaviest planes on the longest flights may eventually be unable to depart during the hottest part of summer days, Radley Horton said, a research scientist at Columbia University’s Earth Institute. He also pointed out that a no-fly window of even a few hours at a particular airport could have a ripple effect across airline operations.
   With forecasts predicting record-breaking temperatures in Phoenix on Tuesday—and some flights being canceled pre-emptively—many passengers stayed away from the airport entirely.
   
选项
答案G
解析 由题干关键词Radley Horton可定位到倒数第二段。由最后一句a no-fly window of even a few hours at a particular airport could have a ripple effect across airline operations．．．(在某个机场哪怕停飞数小时，都会对航空公司的运营产生连锁反应……)可推断出G项为正确答案。其中，have a knock-on effect on是have a ripple effect的同义替换，意为“对……产生连锁反应”，故本题选G。
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