Wu Yan wants to buy dress for her mother on Mother's Day.
A:an; the
B:/; a
C:a; /
D:the; a
2011中国城市竞争力测评纳入了“幸福感”指标,北京的产业层次竞争力排名第一,而在幸福指数一项排名第9。其原因为()