研究下列表格,最符合其内容的学习主题是( )
A:清朝民族关系的发展
B:边疆商业贸易的繁荣
C:统一多民族国家巩固
D:民族地区经济的发展
We were dying to hear the announcement of the winner of the race.
90-23-38=( )