单项选择题
A.1-2n-1 B.-2n-1 C.-2n-1-1 D.-2n
A.{1,2,3,4,5,6,7} B.{1,2,3,4,4,5,6,7,7,7} C.{1,2,3,4,5,6,7,9} D.{4,7,5,1,7,6,2,7,3,4}
A.few B.fraudulent C.normal D.structured