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若集合A具有以下性质：①0∈A，1∈A；②若x，y∈A，则x-y∈A，且x≠0时， 1 x ∈A ．则称集合A是“好集”． （Ⅰ）分别判断集合B={-1，0，1}，有理数集Q是否是“好集”，并说明理由； （Ⅱ）设集合A是“好集”，求证：若x，y∈A，则x+y∈A； （Ⅲ）对任意的一个“好集”A，分别判断下面命题的真假，并说明理由． 命题p：若x，y∈A，则必有xy∈A； 命题q：若x，y∈A，且x≠0，则必有 y x ∈A ．
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