A.MN                 B.MN               C.NM                D.NM

A.4                     B.3                    C.2                    D.1

(2)由(1)你发现当集合M中含有n个元素，则集合M有多少个子集？

A.P={1,,π},Q={π,1,｜｜}                  B.P={π},Q={3.141 59}

C.P={2,3},Q={(2，3)}                             D.P={x｜-1＜x≤1,x∈N},Q={1}