单选题
A rectangular label is attached to a right circular cylinder with radius r．The label，which encircles the cylinder without overlap，has width w and an area equal to the area of the base of the cylinder．
A rectangular label is attached to a right circular cylinder with radius r．The label，which encircles the cylinder without overlap，has width w and an area equal to the area of the base of the cylinder．
【正确答案】
B
【答案解析】一个长方形的检签贴在半径为r的直圆柱上。该标签围绕圆柱体一周且不重叠，其宽度为w，面积等于圆柱体底面的面积。
由于该标签围绕圆柱体且不重叠，所以其长度等于圆柱体底面的周长=2πr，则其面积=2πr?w(因为这是一个长方形标签)，圆柱体底面积为πr2，由题意可得：
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由于该标签围绕圆柱体且不重叠，所以其长度等于圆柱体底面的周长=2πr，则其面积=2πr?w(因为这是一个长方形标签)，圆柱体底面积为πr2，由题意可得：
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