Question

已知集合A＝{1,2,3,4,5}，B＝{(x，y)|x∈A，y∈A，x－y∈A}；则B中所含元素的个数为(　　)

A．3                                    B．6

C．8                                    D．10

Answer 1

 [答案]　D

[解析]　x＝5，y＝1,2,3,4　x＝4，y＝1,2,3，x＝3，y＝1,2，x＝2，y＝1共10个