1992 AMC 8 第 20 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
20.
下列哪一种由全等正方形组成的图案，不能沿所示线折成一个立方体？
Which pattern of identical squares could not be folded along the lines shown to form a cube?
小提示：
立方体有 个面，所以每个图案都有 个正方形；在脑中试着把它们折起来。
A cube has faces, so each pattern has squares; try folding each one up in your mind
大提示：
追踪每个正方形折叠后落在哪个面上；如果两个正方形会盖到同一个面上，图案就失败。
Track where each square lands as the pattern folds; a pattern fails when two squares would cover the same face
解答：
五个图案都由 个正方形组成。把 A、B、C 和 E 折叠时，各正方形能分别覆盖立方体的六个面。
对图案 D，无论怎样折叠，都会迫使两个正方形落在同一个面上而重叠，所以不能形成立方体。
所以正确答案是 D。
Each of the five patterns has squares. Folding patterns (A), (B), (C), and (E) wraps the squares neatly onto the six faces of a cube.
For pattern (D), any attempt to fold forces two of the squares to land on the same face, so they overlap and no cube can be formed.
Thus, the correct answer is D .
其他年份的第 20 题
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