A square paper is folded once vertically and then once horizontally. A hole is punched through all layers, away from every fold and edge. How many holes appear after unfolding?

Answer: B. 4

When a square paper is folded once vertically, it forms 2 layers, and when it is folded again horizontally, the number of layers doubles to 4. When one hole is punched through all four layers, the punch passes through each layer. Therefore, when the paper is completely unfolded, 4 separate holes appear. The shortcut is 2^n, where n is the number of folds.

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