Determinati proprietate caracteristica a elementelor multimii

a) A ={0, 1, 2, 3, 4, 5, 6}

b) B ={15, 30, 45, 60, 75, 90}

c) A ={3, 6, ,9}

d) C ={3, 4, 5, 6, 7, 8}.