Question

B可不可以等于{1,2,3,4}

Answer 1

15个,可以等于{1,2,3,4},分别是{1}、{2}、{3}、{4}、{1,2}、{1,3}、{1,4}、{2,3}、{2,4}、{3,4}、{1,2,3}、{1,2,4}、{1,3,4}、{2,3,4}、{1,2,3,4}