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  3. Recent research from animal behaviorists suggests that "as the crow flies" should no longer be taken to mean "the shortest dista

Recent research from animal behaviorists suggests that "as the crow flies" should no longer be taken to mean "the shortest dista

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问题    Recent research from animal behaviorists suggests that "as the crow flies" should no longer be taken to mean "the shortest distance between two points." Zoologists at Oxford University,【C1】______conducted an eighteen-month【C2】______of homing pigeons, have concluded that under some circumstances, pigeons follow【C3】______visual landmarks to find their way home【C4】______than taking the shortest, most direct route.【C5】______for their ability to navigate long distances, homing pigeons use the【C6】______of the sun and stars, their inbuilt compasses, and perhaps also their sense of smell to direct their flight over long【C7】______or on a journey for the first time.【C8】______, different factors appear to affect a pigeon’s navigation【C9】______it is released close to its【C10】______. Animal behaviorists reached this【C11】______after attaching small global positioning devices to the backs of pigeons and releasing them a few miles from their home. These devices enabled the scientists to【C12】______the precise location of each pigeon every second of【C13】______flight. Each pigeon was tracked for approximately twenty flights from the【C14】______point. For the first several flights, each bird’s path【C15】______significantly from the paths it had taken【C16】______. Subsequently,【C17】______, the bird would tend to follow the same path,【C18】______after flight, even though that path was not always the most direct route home. The scientists concluded that pigeons use a【C19】______of familiar visual landmarks to find their way when they are near their home rather than relying primarily on compass navigation. Major highways are one【C20】______landmark. Almost comically, some of the pigeons followed the path of a major highway they could see below them, turning where the road turned, and even following the circular path of the exit ramps.
【C9】
选项 A、when
B、until
C、still
D、since
答案A
解析 前面提到了长距离飞行，此处是说当信鸽被放飞到家附近的地方时，它的导航能力似乎会受不同因素的影响。因此应选表示时间的连词when“当……时”，因此答案为A。
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