在图示三个振动系统中,物块的质量均为 m,弹簧的刚性系数均为k,摩擦和弹簧的质量不计。设图(a)、(b)、(c)中弹簧的振动频率分别为f1、f2、f3,则三者的关系为()。
A. f1=f2≠f3
B. f1≠f2=f3
C. f1=f2=f3
D. f1≠f2≠f3
In addition, Froebel was concerned that the spread of industrialization would negatively affect the family, but he believed that______.
A. kindergartens could increase the social ability of mothers and children
B. kindergartens were associated with liberalism and free-thinking
C. they would not be banned by the Prussian government in the future
D. kindergartens could increase the social position of mothers and children