Gaokao Math Practice Question
1. （5 分）已知集合 $A=\{1,2,3,4,5\}, B=\{(x, y) \mid x \in A, y \in A, x-y \in A\}$, 则 $B$ 中所含元素的个数为（ $)$
- A.3
- B.6
- C.8
- D.10
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