简述我国通用铁路货车滚动轴承的种类？
参考答案：
目前我国铁路货车通用滚动轴承有3种：197726型、SKF197726型、352226X2-2RZ型。
He had wonderful childhood, _____ with his mother to all corners of the world. [ ]
A. travel
B. to travel
C. traveled
D. traveling
国家不承担行政赔偿责任的情形有哪三种？
