如果m×4=n×5，
那么m：n=5：4，
即mn=54；
故答案为：54．
By careful observation and precise calculation, Nicolaus Copernicus _____ that there is no one center
in the universe and the sun is the center of the solar system. [ ]
A. believed
B. thought
C. concluded
D. imagined
市场经济运行的微观基础以及市场活动最基本的主体是( )
A．产品
B．企业
C．生产部门
D．管理部门
