滚动轴承与滑动轴承的根本区别是以______摩擦代替了滑动摩擦。
参考答案：滚动
Go on climbing to the top of the peak, and you will see all the____ hills.
A．surround
B．surrounded
C．surrounding
D．being surrounded
钨板氩弧焊的电极材料，目前主要有纯钨钍钨和（）等三种。
