向心轴承主要承受径向载荷，所以叫（）。
A、滑动轴承
B、止推轴承
C、径向轴承
D、滚动轴承
参考答案：C
转向灯光闪光频率一般为多少？受何因素影响？
Which of the following people could tell the difference between a cultured pearl and an organic pearl
A．Scuba diver.
B．Fisherman.
C．Jeweler.
D．Clerk.
