Naked Pairs puzzles
The Naked Pairs method can be used when two unfilled adjacent cells (adjacent means in the same row, column, or box as one another) have the same set of candidates, and each of the cells only has two candidates. Since the cells can't contain the same number, both of the candidates must be in one of these cells, so these numbers can be eliminated as a candidate from any cell in the same row/column/box as both of the unfilled cells. For example, if the cells are in the same box, all other cells in that box can not contain the two candidates, so those numbers can be removed as a candidate from every other cell in the box.
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A
B
C
Using the Naked Pairs method, which number goes in cell B4?
Example:
