单选题 ( 2.5 分 ) 设集合A={1,a},则A的幂集P()=( )?
A. {{1},{a}}
B. {∅,{1},{a}}
C. {∅,{1},{a},{1,a}}
D. {{1},{a},{1,a}}
单选题 ( 2.5 分 ) 集合A={1,2,3,4,5,6,7},下面哪个集合是集合A的划分()?
A. {{1,2,3},{1,4,5,6},{2,3,5,7}}
B. {∅,{1,2,3,4},{5,6,7}}
C. {{1,2,3},{4,5},{6,7}}
D. {{1,2,6},{3,4,5}}