问题 选择题
在①1⊆{0,1,2,3};②{1}∈{0,1,2,3};③{0,1,2,3}⊆{0,1,2,3};④∅⊊{0},上述四个关系中,错误的个数是(  )
A.1个B.2个C.3个D.4个
答案

答案:B

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