练习题 · 英文原题 · SEL-TS-TST-18
A square sheet of paper is marked in a 6 by 6 grid. It is folded twice, and then two holes are punched through all the layers.
The paper is unfolded. Which picture shows the holes in the unfolded sheet?
查看答案与解析（英文）
答案: A
Answer: A
Undo the folds in reverse order. Each fold line works like a mirror.
- The punched holes are in column 4, row 5 and column 6, row 6.
- Open fold 2 (the top half comes back up). Each hole is copied in the line between rows 3 and 4: row 5 matches row 2 and row 6 matches row 1. Holes now: column 4 rows 2 and 5; column 6 rows 1 and 6.
- Open fold 1 (the left half comes back). Every hole so far is copied in the line between columns 3 and 4: column 4 matches column 3 and column 6 matches column 1. This adds column 3 rows 2 and 5, and column 1 rows 1 and 6.
- There are 8 holes: row 1 columns 1 and 6; row 2 columns 3 and 4; row 5 columns 3 and 4; row 6 columns 1 and 6.
Why the other options are wrong
- B: This shows holes only in the bottom rows, but the top half of the sheet was folded down and punched too.
- C: This misses two holes: when fold 1 is opened, the holes in rows 1 and 2 must be copied too, so the top-left quarter needs holes in column 1 row 1 and column 3 row 2.
- D: The holes have been slid across and up instead of flipped over the fold lines.