Detailed studies of the tribe by the food scientists at Athe University of London showed that gathering is a more productive sou

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问题 Detailed studies of the tribe by the food scientists at Athe University of London showed that gathering is a more productive source of food Bthan is hunting. An hour of hunting yields Con average about 100 edible calories Das an hour of gathering produces 240.

选项 A、 
B、 
C、 
D、 

答案D

解析 根据上下文意思,“An hour of hunting yields on average about…produces 240”表示一种对比关系,引出相反或不同的事实,因此应将as改为whereas或while。
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